Ventilation Amplitude Research Articles

Physiological effects of exercising at different intensities wearing surgical or double-layer cotton facemasks compared to not wearing a mask

ABSTRACT Since the beginning of the SARS-CoV-2 pandemic, the community use of facemasks has been widely recommended. However, their use during exercise has raised safety concerns. Thus, we compared the physiological differences between exercising wearing a surgical (SM) or a double-layer-cotton (DLC) facemask and not wearing a mask (NM). Sixteen volunteers underwent 4 bouts of cycling-based exercise, which consisted of two different intensities: light-to-moderate and moderate-to-high. Facemasks were used as follows: bout-1 and 4: NM; bout-2: SM or DLC and bout-3: DLC or SM. Ventilatory, metabolic, pulmonary gas exchange (PGE) and perceptual variables were collected. At both exercise intensities compared to NM, both facemasks induced similar ventilatory adaptations, increasing inspiratory time and tidal volume and decreasing breathing frequency. Effect sizes (ES) were larger for DLC than for SM. At moderate-to-high, both facemasks reduced the minute ventilation, whereas at light-to-moderate, it was only seen with DLC. End tidal and mixed CO2 pressures, as well as the difference between them, increased with both facemasks. Again, ES was larger for DLC than SM. No relevant oxygen saturation drop was observed with both facemaks and exercise intensities. A small ES increament in VO2 and VCO2 were seen with both facemasks. Effort perception increased at moderate-to-high for both exercise intensities, buth larger EF were with DLC than SM . DLC increased facial temperature during both exercise intensities. In conclusion, ventilatory adjustments imposed during facemask exercise influenced PGE and metabolic and perceptual changes. Larger ES were mostly seen for DLC than SM. Abbreviations: B f : Breathing frequency.; CPET: Cardiopulmonary exercise test.; CI: Confidence interval.; DLC: Double-layer cotton.; ETCO2: End tidal CO2 pressure.; ES: Effect size.; ΔET-PECO2: Difference between ETCO2 and PECO2.; FMMT: Facemask microclimate temperature.; H R : Heart rate.; IQR: Interquartile range.; NM: No mask.; PECO2: Mixed-expired CO2 pressure.; RER: Respiratory exchange ratio.; RPE: Rate of perceived effort.; SD: Standard deviation.; SM: Surgical Mask.; SpO2: Oxygen saturation.; STP: Subjective thermal perception.; Ti/TTOT: Duty cycle.; VE: Minute ventilation.; VCO2: Carbon dioxide output.; VO2: Oxygen uptake.; V T : Tidal volume.; VT: Ventilatory threshold. Highlights Facemasks affect the breathing pattern by changing the frequency and amplitude of pulmonary ventilation. The augmented ventilatory work increases VO2, VCO2, and RPE and promotes nonconcerning drops in SpO2 and CO2 retention. Increased inspiratory and expiratory pressure can account for the reduction in pulmonary physiological dead space.

Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure.

Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet. Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure. Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of EIT measurements was 53 ± 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks. Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort. Clinical trial registered with www.clinicaltrials.gov (NCT02962505).

The effects of sinusoidal linear drifts on the estimation of cardiorespiratory dynamic parameters during sinusoidal workload forcing: a simulation study

This study aimed at investigating whether: 1) different sinusoidal linear drifts would affect the estimation of the dynamic parameters amplitude (A) and phase lag (φ) of minute ventilation (V˙E), oxygen uptake, carbon dioxide production and heart rate (HR) sinusoidal responses when the frequency analysis technique (F) is performed; 2) the Marquardt-Levenberg non-linear fitting technique (ML) would provide more precise estimations of A and φ of drifted sinusoidal responses compared to F.For each cardiorespiratory variable, fifteen responses to sinusoidal forcing of different sinusoidal periods were simulated by using a first-order dynamic linear model. A wide range of linear drifts were subsequently applied. A and φ were computed for all drifted and non-drifted responses by using both F (AF and φF) and ML (AML and φML).For non-drifted responses, no differences between AF vs AML and φF vs φML were found. Whereas AF and φF were affected by the sinusoidal linear drifts, AML and φML were not. Significant interaction effects (technique x drift) were found for A (P < 0.001; ƞP2 > 0.247) and φ (P < 0.001; ƞP2 > 0.851). Higher goodness of fit values were observed when using ML for drifted V˙E and HR responses only.The present findings suggest ML as a recommended technique to use when sinusoidal linear drifts occur during sinusoidal exercise, and provide new insights on how to analyse drifted cardiorespiratory sinusoidal responses.

Respiratory responses to external ammonia in zebrafish (Danio rerio)

The effects of high external ammonia (HEA) exposure on breathing and the potential involvement of ammonia transporting Rh proteins in ammonia sensing were assessed in larval and adult zebrafish. Acute exposure of adults to either 250 or 500 μM (NH4)2SO4 caused increases in ventilation amplitude (AVENT) without affecting frequency (fVENT), resembling the ventilatory response to hypercapnia rather than hypoxia, during which fVENT was increased exclusively. The hyperventilatory response to HEA was prevented by hyperoxia, indicating that control of breathing through ammonia sensing is likely secondary to O2 chemoreception. Neuroepithelial cells (NECs) isolated from gill filaments exhibited a significant increase of intracellular [Ca2+] in response to 1 mM NH4Cl but this response was small (roughly 30%) compared to the response to hypercapnia (37.5 mmHg; ~800% increase). Immunohistochemistry (IHC) failed to reveal the presence of Rh proteins (Rhcgb, Rhbg or Rhag) in gill filament NECs. Knockout of rhcgb did not affect the ventilatory response of adults to HEA. Larvae at 4 days post fertilization (dpf) responded to HEA with increases in fVENT (AVENT was not measured). The hyperventilatory response of larvae to HEA was attenuated (60% reduction) after treatment from 0 to 4 dpf with the sympathetic neurotoxin 6-hydroxydopamine. In larvae, Rhcgb, Rhbg and Rhag were undetectable by IHC in cutaneous NECs yet the fVENT to HEA following Rhbg knockdown was slightly (22%) attenuated. Thus, the hyperventilatory response to external ammonia in adult zebrafish, while apparently initiated by activation of NECs, does not require Rhcgb, nor is the entry of ammonia into NECs reliant on other Rh proteins. The lack of colocalization of Rh proteins with NECs suggests that the entry of ammonia into NECs in larvae, also is not facilitated by this family of ammonia channels.

Postprandial cardiorespiratory responses and the regulation of digestion-associated tachycardia in Nile tilapia (Oreochromis niloticus).

Cardiorespiratory adjustments that occur after feeding are essential to supply the demands of digestion in vertebrates. The well-documented postprandial tachycardia is triggered by an increase in adrenergic activity and by non-adrenergic non-cholinergic (NANC) factors in mammals and crocodilians, while it is linked to a withdrawal of vagal drive and NANC factors in non-crocodilian ectotherms-except for fish, in which the sole investigation available indicated no participation of NANC factors. On the other hand, postprandial ventilatory adjustments vary widely among air-breathing vertebrates, with different species exhibiting hyperventilation, hypoventilation, or even no changes at all. Regarding fish, which live in an environment with low oxygen capacitance that requires great ventilatory effort for oxygen uptake, data on the ventilatory consequences of feeding are also scarce. Thus, the present study sought to investigate the postprandial cardiorespiratory adjustments and the mediation of digestion-associated tachycardia in the unimodal water-breathing teleost Oreochromis niloticus. Heart rate (fH), cardiac autonomic tones, ventilation rate (fV), ventilation amplitude, total ventilation and fH/fV variability were assessed both in fasting and digesting animals under untreated condition, as well as after muscarinic cholinergic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that digestion was associated with marked tachycardia in O. niloticus, determined by a reduction in cardiac parasympathetic activity and by circulating NANC factors-the first time such positive chronotropes were detected in digesting fish. Unexpectedly, postprandial ventilatory alterations were not observed, although digestion triggered mechanisms that were presumed to increase oxygen uptake, such as cardiorespiratory synchrony.

Interplay Between Optimal Ventilation and Gas Transport in a Model of the Human Lung.

Ventilation is at the origin of a spending of energy coming from air circulation in the bronchial tree and from the mechanical resistance of the tissue to motion. Both amplitude and frequency of ventilation are submitted to a trade-off related to this energy, but they are also submitted to a constraint linked to the function of the lung: to transport enough oxygen and carbon dioxide in order to respect metabolism needs. We propose a model for oxygen and carbon dioxide transport in the lung that accounts for the core physical phenomena: lung's tree-like geometry, transport of gas by convection and diffusion, exchanges with blood and a sinusoidal ventilation. Then we optimize the power dissipated by the ventilation of our model relatively to ventilation amplitude and period under gas flow constraints. Our model is able to predict physiological ventilation properties and brings interesting insights on the robustness of different regimes. Hence, at rest, the power dissipated depends very little on the period near the optimal value. Whereas, at strong exercise any shift from the optimal has dramatic effect on the power. These results are fully coherent with the physiological observation and raises the question: how the control of ventilation could select for the optimal configuration? Also, interesting insights about pathologies affecting ventilation could be derived, and our model might give insights on therapeutical responses, with specific breathing strategies or for better driving mechanical ventilation.

Treatment with the selective serotonin reuptake inhibitor, fluoxetine, attenuates the fish hypoxia response.

The selective serotonin reuptake inhibitor (SSRI) fluoxetine (FLX), the active ingredient of the antidepressant drug Prozac, inhibits reuptake of the neurotransmitter, serotonin (5-HT; 5-hydroxytryptamine), into cells by the 5-HT transporter (SERT). Given the role of 5-HT in oxygen detection and the cardiovascular and ventilatory responses of fish to hypoxia, we hypothesized that treatment of the Gulf toadfish, Opsanus beta, with FLX would interfere with their response to hypoxia. Toadfish treated intra-arterially with 3.4 μg.g−1 FLX under normoxic conditions displayed a transient tachycardia and a biphasic caudal arterial blood pressure (PCA) response that are in direct conflict with the typical hypoxia response. Fish injected intraperitoneally with FLX under normoxia had resting cardiovascular and ventilatory parameters similar to controls. Upon exposure to hypoxia, control toadfish exhibit a significant bradycardia, reduction in PCA and an increase in ventilatory amplitude (VAMP) without any changes in ventilatory frequency (fV). Fish treated IP with 10 μg.g−1 FLX showed an interference in the cardiovascular and ventilatory response to hypoxia. Interestingly, when treated with 25 μg.g−1 FLX, the bradycardia and VAMP response to hypoxia were similar to control fish while the PCA response to hypoxia was further inhibited. These results suggest that SERT inhibition by FLX may hinder survival in hypoxia.

Control of cardiorespiratory function in response to hypoxia in an air-breathing fish, the African sharptooth catfish, Clarias gariepinus

We evaluated the role of the first pair of gill arches in the control of cardiorespiratory responses to normoxia and hypoxia in the air-breathing catfish, Clarias gariepinus. An intact group (IG) and an experimental group (EG, bilateral excision of first gill arch) were submitted to graded hypoxia, with and without access to air. The first pair of gill arches ablations reduced respiratory surface area and removed innervation by cranial nerve IX. In graded hypoxia without access to air, both groups displayed bradycardia and increased ventilatory stroke volume (VT), and the IG showed a significant increase in breathing frequency (fR). The EG exhibited very high fR in normoxia that did not increase further in hypoxia, this was linked to reduced O2 extraction from the ventilatory current (EO2) and a significantly higher critical O2 tension (PcO2) than the IG. In hypoxia with access to air, only the IG showed increased air-breathing, indicating that the first pair of gill arches excision severely attenuated air-breathing responses. Both groups exhibited bradycardia before and tachycardia after air-breaths. The fH and gill ventilation amplitude (VAMP) in the EG were overall higher than the IG. External and internal NaCN injections revealed that O2 chemoreceptors mediating ventilatory hypoxic responses (fR and VT) are internally oriented. The NaCN injections indicated that fR responses were mediated by receptors predominantly in the first pair of gill arches but VT responses by receptors on all gill arches. Receptors eliciting cardiac responses were both internally and externally oriented and distributed on all gill arches or extra-branchially. Air-breathing responses were predominantly mediated by receptors in the first pair of gill arches. In conclusion, the role of the first pair of gill arches is related to: (a) an elevated EO2 providing an adequate O2 uptake to maintain the aerobic metabolism during normoxia; (b) a significant bradycardia and increased fAB elicited by externally oriented O2 chemoreceptors; (c) increase in the ventilatory variables (fR and VAMP) stimulated by internally oriented O2 chemoreceptors.

Does ammonia trigger hyperventilation in the elasmobranch, Squalus acanthias suckleyi?

We examined the ventilatory response of the spiny dogfish, to elevated internal or environmental ammonia. Sharks were injected via arterial catheters with ammonia solutions or their Na salt equivalents sufficient to increase plasma total ammonia concentration [TAmm]a by 3–5 fold from 145±21μM to 447±150μM using NH4HCO3 and a maximum of 766±100μM using (NH4)2SO4. (NH4)2SO4 caused a small increase in ventilation frequency (+14%) and a large increase in amplitude (+69%), while Na2SO4 did not. However, CO2 partial pressure (PaCO2) also increased and arterial pHa and plasma bicarbonate concentration ([HCO3−]a) decreased. NH4HCO3 caused a smaller increase in plasma ammonia resulting in a smaller but significant, short lived increases in ventilation frequency (+6%) and amplitude (36%), together with a rise in PaCO2 and [HCO3−]a. Injection with NaHCO3 which increased pHa and [HCO3−]a did not change ventilation. Plasma ammonia concentration correlated significantly with ventilation amplitude, while ventilation frequency showed a (negative) correlation with pHa. Exposure to high environmental ammonia (1500μM NH4HCO3) did not induce changes in ventilation until plasma [TAmm]a increased and ventilation amplitude (but not frequency) increased in parallel. We conclude that internal ammonia stimulates ventilation in spiny dogfish, especially amplitude or stroke volume, while environmental ammonia only stimulates ventilation after ammonia diffuses into the bloodstream.

Effects of intracerebroventricular administered fluoxetine on cardio-ventilatory functions in rainbow trout (Oncorhynchus mykiss)

Fluoxetine (FLX) is a selective serotonin (5-HT) reuptake inhibitor present in the aquatic environment which is known to bioconcentrate in the brains of exposed fish. FLX acts as a disruptor of various neuroendocrine functions in the brain, but nothing is known about the possible consequence of FLX exposure on the cardio-ventilatory system in fish. Here we undertook to investigate the central actions of FLX on ventilatory and cardiovascular function in unanesthetized rainbow trout (Oncorhynchus mykiss). Intracerebroventricular (ICV) injection of FLX (dosed between 5 and 25μg) resulted in a significantly elevated total ventilation (VTOT), with a maximum hyperventilation of +176% (at a dose of 25μg) compared with vehicle injected controls. This increase was due to an increase in ventilatory amplitude (VAMP: +126%) with minor effects on ventilatory frequency. The highest dose of FLX (25μg) produced a significant increase in mean dorsal aortic blood pressure (PDA: +20%) without effects on heart rate (ƒH). In comparison, intra-arterial injections of FLX (500–2500μg) had no effect on ventilation but the highest doses increased both PDA and ƒH. The ICV and IA cardio-ventilatory effects of FLX were very similar to those previously observed following injections of 5-HT, indicating that FLX probably acts via stimulating endogenous 5-HT activity through inhibition of 5-HT transporter(s).Our results demonstrate for the first time in fish that FLX administered within the brain exerts potent stimulatory effects on ventilation and blood pressure increase. The doses of FLX given to fish in our study are higher than the brain concentrations of FLX in fish that result from acute exposure to FLX through the water. Nonetheless, our results indicate possible disrupting action of long term exposure to FLX discharged into the environment on central target sites sensitive to 5-HT involved in cardio-ventilatory control.

Increased ventilation by fish leads to a higher risk of parasitism.

BackgroundFish are common intermediate hosts of trematode cercariae and their gills can potentially serve as important sites of penetration by these larval stages. We experimentally tested the hypothesis that volume of ventilation flow across the gills contributes to acquisition of these parasites by fish. We manipulated the intensity of ventilation by using different oxygen concentrations.MethodsJuvenile Oncorhynchus mykiss were individually exposed for 10 minutes to a standard dose of Diplostomum pseudospathaceum cercariae at three levels of oxygen concentration, 30, 60 and 90%. Ventilation amplitude (measured as a distance between left and right operculum), operculum beat rate, and the number of cercariae established in the eyes of fish were recorded.ResultsFish reacted to low oxygen concentration with wider expansion of opercula (but not with increasing beat rate), leading to an increase in ventilation volume. As expected, the intensity of infection increased with decreasing oxygen saturation—probably due to a higher exposure to cercariae caused by increased ventilation under low oxygen concentrations. The number of cercariae acquired by an individual fish was positively correlated with ventilation amplitude and with ventilation volume, but not with operculum beat rate. However, even though the infection rate increased under these circumstances, the proportion of larval trematodes successfully establishing in fish eyes decreased with increasing ventilation volume, suggesting that the high flow velocity, although increasing host exposure to cercarial parasites, may interfere with the ability of these parasites to penetrate their hosts. There was no difference in the behaviour of trematode cercariae exposed to low and high oxygen concentrations.ConclusionA reduction in oxygen saturation resulted in an increase in ventilation volume across the gills and in doing so an increase in the exposure of fish to cercariae. A significant correlation between ventilation volume and parasitism represents the first experimental evidence that this physiological mechanism generates variation in transmission of parasites to fish hosts. Other factors that modify ventilation flow, e.g. physiological or social stressors, are expected to produce similar effects on the transmission success of the parasites penetrating fish hosts using the gills.

Isocitrate supplementation promotes breathing generation, gasping, and autoresuscitation in neonatal mice

Breathing is a vital function generated and controlled by a brainstem neural network, which is able to adjust its function to fit different metabolic demands. For instance, the pre-Bötzinger complex (preBötC) can respond to low oxygen availability (hypoxia) by an initial increase in rhythm frequency followed by a decrease in respiratory efforts that leads to gasping generation. Gasping is essential for autoresuscitation, which has motivated studies of the cellular mechanisms involved in these processes. Hypoxia has different effects on enzymes that participate in the Krebs cycle. In particular, aconitase is downregulated, whereas isocitrate dehydrogenase is unaffected or upregulated under hypoxic conditions. We hypothesized that the application of isocitrate, the product of aconitase and the substrate of isocitrate dehydrogenase as well as an alternative metabolic substrate, might enhance breathing and render it more resistant to hypoxic insult. We tested the effects of isocitrate applied on brainstem slices containing the preBötC as well as its central effects in vivo using plethysmography. Our results show that isocitrate increases the frequency of fictive eupnea and fictive gasping produced by the preBötC in vitro. Moreover, isocitrate increases the amplitude of ventilation in vivo in normoxia, increases ventilation during gasping, and favors autoresuscitation when animals were subjected to asphyxiation. In conclusion, we have found that isocitrate improves ventilation under both normoxic and hypoxic conditions through a mechanism that involves the preBötC and possibly other respiratory neural networks. Thus, isocitrate would be useful to avoid the failure of gasping generation and autoresuscitation in pathological conditions.

Central ventilatory and cardiovascular actions of serotonin in trout

This study was undertaken to investigate the central actions of 5-HT on ventilatory and cardiovascular variables in the unanesthetized trout. Compared to vehicle, intracerebroventricular injection (ICV) of 5-HT elevated the total ventilation. This elevation was due to its stimulatory action on ventilatory amplitude. Moreover, 5-HT produced a dose-dependent increase in mean dorsal aortic blood pressure (PDA) without change in heart rate (fH). Methysergide, a 5-HT1/5-HT2 receptor antagonist, reduced the hyperventilatory and hypertensive actions of 5-HT. 8-OH-2-(di-n-propylamino) tetralin, a 5-HT1A receptor agonist, increased PDA while α-methyl-5-HT, a 5-HT2 receptor agonist, elevated all ventilatory variables and increased PDA without changing fH. Intra-arterial injection of 5-HT was without effect on ventilation, but 5-HT initially produced hypotension followed by hypertension. These changes were accompanied by tachycardia. It remains to be determined whether endogenous 5-HT within the brain of trout may act as a potent neuroregulator causing stimulatory effects on cardio-ventilatory functions. In the periphery, 5-HT may act as local modulator involved in vasoregulatory mechanisms.

Stress responses in Arctic char (Salvelinus alpinus L.) during hyperoxic carbon dioxide immobilization relevant to aquaculture

Physiological responses during immobilization with hyperoxic hypercapnia were determined in cannulated Arctic char (Salvelinus alpinus) exposed for 10min to mixtures of 10% CO2 in 90% O2 (10:90) or 50% CO2 in 50% O2 (50:50). Results were compared with a previous study on the same group of char using pure CO2 under identical experimental conditions to test the hypothesis that supplemental oxygen may reduce stress and improve welfare during CO2 exposure. While all fish recovered from the two exposures, the time to loss of equilibrium with the 50:50 mixture was significantly shorter than for the 10:90 mixture (143 vs. 276s); and the time to regain equilibrium was longer (2302 vs. 963s). Hypertension and bradycardia developed with 10:90, while 50:50 resulted in tachycardia and unchanged blood pressure. Ventilation frequency and amplitude increased significantly with 10:90, whereas ventilation ceased completely with 50:50. Primary and secondary stress responses were evident during recovery in normoxia in both groups as indicated by elevated heart rate and ventilation and increased plasma cortisol. However, recovery appeared to be faster with the 10:90 mixture because ventilation amplitude and plasma cortisol levels declined more rapidly. Nonetheless, the times to loss of equilibrium recorded here with mixtures of oxygen and carbon dioxide bracket that observed previously with pure CO2. Furthermore, the increase in plasma cortisol was similar or higher in the present study suggesting that while supplemental oxygen does not markedly reduce stress or improve welfare during carbon dioxide immobilization, survival and recovery in normoxia are improved.

Central ventilatory and cardiovascular actions of trout gastrin-releasing peptide (GRP) in the unanesthetized trout

SummaryGastrin-releasing peptide (GRP), a neuropeptide initially isolated from porcine stomach, shares sequence similarity with bombesin. GRP and its receptors are present in the brains and peripheral tissues of several species of teleost fish, but little is known about the ventilatory and cardiovascular effects of this peptide in these vertebrates. The goal of this study was to compare the central and peripheral actions of picomolar doses of trout GRP on ventilatory and cardiovascular variables in the unanesthetized rainbow trout. Compared to vehicle, intracerebroventricular (ICV) injection of GRP (1–50 pmol) significantly elevated the ventilation rate (ƒV) and the ventilation amplitude (VAMP), and consequently the total ventilation (VTOT). The maximum hyperventilatory effect of GRP (VTOT: +225%), observed at a dose of 50 pmol, was mostly due to its stimulatory action on VAMP (+170%) rather than ƒV (+20%). In addition, ICV GRP (50 pmol) produced a significant increase in mean dorsal aortic blood pressure (PDA) (+35%) and in heart rate (ƒH) (+25%). Intra-arterial injections of GRP (5–100 pmol) were without sustained effect on the ventilatory variables but produced sporadic and transient increases in ventilatory movement at doses of 50 and 100 pmol. At these doses, GRP elevated PDA by +20% but only the 50 pmol dose significantly increased HR (+15%). In conclusion, our study suggests that endogenous GRP within the brain of the trout may act as a potent neurotransmitter and/or neuromodulator in the regulation of cardio-ventilatory functions. In the periphery, endogenous GRP may act as locally-acting and/or circulating neurohormone with an involvement in vasoregulatory mechanisms.

Branchial O2 chemoreceptors in Nile tilapia Oreochromis niloticus: Control of cardiorespiratory function in response to hypoxia

This study examined the distribution and orientation of gill O2 chemoreceptors in Oreochromis niloticus and their role in cardiorespiratory responses to graded hypoxia. Intact fish, and a group with the first gill arch excised (operated), were submitted to graded hypoxia and their cardiorespiratory responses (oxygen uptake - V˙O2, breathing frequency - fR, ventilatory stroke volume - VT, gill ventilation - V˙G, O2 extraction from the ventilatory current - EO2, and heart rate - fH) were compared. Their responses to bolus injections of NaCN into the bloodstream (internal) or ventilatory water stream (external) were also determined. The V˙O2 of operated fish was significantly lower at the deepest levels of hypoxia. Neither reflex bradycardia nor ventilatory responses were completely abolished by bilateral excision of the first gill arch. EO2 of the operated group was consistently lower than the intact group. The responses to internal and external NaCN included transient decreases in fH and increases in fR and Vamp (ventilation amplitude). These cardiorespiratory responses were attenuated but not abolished in the operated group, indicating that chemoreceptors are not restricted to the first gill arch, and are sensitive to oxygen levels in both blood and water.

Physiological responses and welfare implications of rapid hypothermia and immobilisation with high levels of CO2 at two temperatures in Arctic char (Salvelinus alpinus)

Carbon dioxide (CO2) is used for immobilisation of Arctic char (Salvelinus alpinus) prior to slaughter at Swedish aquaculture facilities, and fish are routinely exposed to hypothermia in ice water during transport. Yet, information on stress physiological responses to CO2, temperature extremes and their potential interacting effects is scarce for this cold-water species. Here, blood pressure, heart and ventilation rates and plasma variables including ions, haematocrit, glucose and cortisol were measured in cannulated char during exposure to hypothermia (i.e. a rapid temperature drop from 10°C to 0.25°C); as well as to water nearly saturated with CO2 at 10°C and 0.25°C to test the hypothesis that hypothermia alleviates stress responses during CO2 exposure. While all fish maintained equilibrium during the 30min hypothermic challenge, blood pressure, heart and ventilation rates decreased and plasma cortisol increased moderately. CO2 exposure at 10 and 0.25°C resulted in aversive behavioural reactions before equilibrium was irrecoverably lost after 184±14 and 191±9s, respectively. The physiological responses to CO2 exposure were largely similar at both temperatures with elevated cortisol levels, reduced heart and ventilation rates and hypotension; although reductions in ventilation amplitude and arterial pulse pressure were significantly more pronounced at 0.25°C. It is concluded that hypothermia alone is a relatively mild stressor in this species, while CO2 exposure elicits pronounced physiological and behavioural stress responses that are not alleviated by hypothermia.

Sinusoidal high‐intensity exercise does not elicit ventilatory limitation in chronic obstructive pulmonary disease

During exercise at critical power (CP) in chronic obstructive pulmonary disease (COPD) patients, ventilation approaches its maximum. As a result of the slow ventilatory dynamics in COPD, ventilatory limitation during supramaximal exercise might be escaped using rapid sinusoidal forcing. Nine COPD patients [age, 60.2 ± 6.9 years; forced expiratory volume in the first second (FEV(1)), 42 ± 17% of predicted; and FEV(1)/FVC, 39 ± 12%] underwent an incremental cycle ergometer test and then four constant work rate cycle ergometer tests; tolerable duration (t(lim)) was recorded. Critical power was determined from constant work rate testing by linear regression of work rate versus 1/t(lim). Patients then completed fast (FS; 60 s period) and slow (SS; 360 s period) sinusoidally fluctuating exercise tests with mean work rate at CP and peak at 120% of peak incremental test work rate, and one additional test at CP; each for a 20 min target. The value of t(lim) did not differ between CP (19.8 ± 0.6 min) and FS (19.0 ± 2.5 min), but was shorter in SS (13.2 ± 4.2 min; P < 0.05). The sinusoidal ventilatory amplitude was minimal (37.4 ± 34.9 ml min(-1) W(-1)) during FS but much larger during SS (189.6 ± 120.4 ml min(-1) W(-1)). The total ventilatory response in SS reached 110 ± 8.0% of the incremental test peak, suggesting ventilatory limitation. Slow components in ventilation during constant work rate and FS exercises were detected in most subjects and contributed appreciably to the total response asymptote. The SS exercise was associated with higher mid-exercise lactate concentrations (5.2 ± 1.7, 7.6 ± 1.7 and 4.5 ± 1.3 mmol l(-1) in FS, SS and CP). Large-amplitude, rapid sinusoidal fluctuation in work rate yields little fluctuation in ventilation despite reaching 120% of the incremental test peak work rate. This high-intensity exercise strategy might be suitable for programmes of rehabilitative exercise training in COPD.

Sensitivity of ventilation and brain metabolism to ammonia exposure in rainbow trout,Oncorhynchus mykiss

Ammonia has been documented as a respiratory gas that stimulates ventilation, and is sensed by peripheral neuroepithelial cells (NECs) in the gills in ammoniotelic rainbow trout. However, the hyperventilatory response is abolished in trout chronically exposed (1+ months) to high environmental ammonia [HEA; 250 μmol l(-1) (NH4)2SO4]. This study investigates whether the brain is involved in the acute sensitivity of ventilation to ammonia, and whether changes in brain metabolism are related to the loss of hyperventilatory responses in trout chronically exposed to HEA ('HEA trout'). Hyperventilation (via increased ventilatory amplitude rather than rate) and increased total ammonia concentration ([TAmm]) in brain tissue were induced in parallel by acute HEA exposure in control trout in a concentration-series experiment [500, 750 and 1000 μmol l(-1) (NH4)2SO4], but these inductions were abolished in HEA trout. Ventilation was correlated more closely to [TAmm] in brain rather than to [TAmm] in plasma or cerebrospinal fluid. The close correlation of hyperventilation and increased brain [TAmm] also occurred in control trout acutely exposed to HEA in a time-series analysis [500 μmol l(-1) (NH4)2SO4; 15, 30, 45 and 60 min], as well as in a methionine sulfoxamine (MSOX) pre-injection experiment [to inhibit glutamine synthetase (GSase)]. These correlations consistently suggest that brain [TAmm] is involved in the hyperventilatory responses to ammonia in trout. The MSOX treatments, together with measurements of GSase activity, TAmm, glutamine and glutamate concentrations in brain tissue, were conducted in both the control and HEA trout. These experiments revealed that GSase plays an important role in transferring ammonia to glutamate to make glutamine in trout brain, thereby attenuating the elevation of brain [TAmm] following HEA exposure, and that glutamate concentration is reduced in HEA trout. The mRNAs for the ammonia channel proteins Rhbg, Rhcg1 and Rhcg2 were expressed in trout brain, and the expression of Rhbg and Rhcg2 increased in HEA trout, potentially as a mechanism to facilitate the efflux of ammonia. In summary, the brain appears to be involved in the sensitivity of ventilation to ammonia, and brain ammonia levels are regulated metabolically in trout.

Central ventilatory and cardiovascular actions of angiotensin peptides in trout

In the brains of teleosts, angiotensin II (ANG II), one of the main effector peptides of the renin-angiotensin system, is implicated in various physiological functions notably body fluid and electrolyte homeostasis and cardiovascular regulation, but nothing is known regarding the potential action of ANG II and other angiotensin derivatives on ventilation. Consequently, the goal of the present study was to determine possible ventilatory and cardiovascular effects of intracerebroventricular injection of picomole doses (5-100 pmol) of trout [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, ANG IV, and ANG 1-7 into the third ventricle of unanesthetized trout. The central actions of these peptides were also compared with their ventilatory and cardiovascular actions when injected peripherally. Finally, we examined the presence of [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, and ANG IV in the brain and plasma using radioimmunoassay coupled with high-performance liquid chromatography. After intracerebroventricular injection, [Asn(1)]-ANG II and [Asp(1)]-ANG II two ANG IIs, elevated the total ventilation through a selective stimulatory action on the ventilation amplitude. However, the hyperventilatory effect of [Asn(1)]-ANG II was threefold higher than the effect of [Asp(1)]-ANG II at the 50-pmol dose. ANG III, ANG IV, and ANG 1-7 were without effect. In addition, ANG IIs and ANG III increased dorsal aortic blood pressure (P(DA)) and heart rate (HR). After intra-arterial injections, none of the ANG II peptides affected the ventilation but [Asn(1)]-ANG II, [Asp(1)]-ANG II, and ANG III elevated P(DA) (50 pmol: +80%, +58% and +48%, respectively) without significant decrease in HR. In brain tissue, comparable amounts of [Asn(1)]-ANG II and [Asp(1)]-ANG II were detected (ca. 40 fmol/mg brain tissue), but ANG III was not detected, and the amount of ANG IV was about eightfold lower than the content of the ANG IIs. In plasma, ANG IIs were also the major angiotensins (ca. 110 fmol/ml plasma), while significant but lower amounts of ANG III and ANG IV were present in plasma. In conclusion, our study suggests that the two ANG II isoforms produced within the brain may act as a neurotransmitter and/or neuromodulator to regulate the cardioventilatory functions in trout. In the periphery, two ANG IIs and their COOH-terminal peptides may act as a circulating hormone preferentially involved in cardiovascular regulations.