Respiratory Adjustments Research Articles

Found in translation: neural feedback from exercising muscles

Found in translation: neural feedback from exercising muscles

Immediate and Sustained Changes in Tongue Movement with an Experimental Palatal “Fistula”: A Case Study

To determine the immediate and longer-term effect(s) on tongue movement following the placement of an experimental opening through a palatal obturator (replicate of subject's prosthesis) worn by an adult male with an unrepaired cleft of the hard and soft palate. Tongue movements associated with an anterior experimental opening of 20 mm(2) were examined under three conditions: a control condition in which the subject wore the experimental obturator completely occluded, a condition immediately after drilling the experimental openings through the obturator, and a condition after 5 days in which the subject wore the experimental obturator with the experimental opening. An Electromagnetic Articulograph was used for obtaining tongue movements during speech. The findings partly revealed that the immediate introduction of a perturbation to the speech system (experimental fistula) had a temporary effect on tongue movement. After sustained perturbation (for 5 days), the system normalized (going back toward control condition's behavior). Perceptual data were consistent with kinematic tongue movement direction in most of the cases. Although the immediate response can be interpreted as indicative of the subject's attempts to move the tongue toward the opening to compensate for air loss, the findings following a sustained perturbation indicate that with time, other physiological adjustments (such as respiratory adjustments, for example) may help reestablish the requirements of a pressure-regulating system.

Métabosensibilité musculaire et adaptations physiologiques au cours de l’exercice

The first role played by group III (thin myelinated) and group IV (unmyelinated) afferent fibres from skeletal muscle is to transmit nociceptive information from muscle to the central nervous system. The second role of these free endings located in the interstitium of the muscle is to induce cardiovascular and respiratory adjustments during muscular exercise. These respiratory and circulatory responses during muscular exercise may be reflexly induced via muscular afferents. Indeed, static contraction of hindlimb muscles in anaesthetised mammals has been shown to reflexly increase the ventilatory function, the myocardial contractility and heart rate. The mechanical muscle deformation and the accumulation of metabolites in its intersitium are the cause of raised activity in small nerve fibres which in turn induces the physiological responses. It is also admitted that the central locomotor areas on the medullary and spinal neuronal pools control ventilatory and cardiovascular function during exercise. This mechanism is called "central command". Furthermore, adjustments of the locomotor activity during exercise is mediated by the thinly myelinated and unmyelinated fibres with endings in the working muscle. These fibres, also called "metaboreceptor" may be responsible of the coupling between the ventilation and the locomotion. Thickly myelinated muscle afferents (i.e. group I and II) appear to play little role in causing the reflex autonomic responses to contraction.

Cobalt injections into the pedunculopontine nuclei attenuate the reflex diaphragmatic responses to muscle contraction in rats.

Previous studies have suggested that neurons in the pedunculopontine nucleus (PPN) are activated during static muscle contraction. Furthermore, activation of the PPN, via electrical stimulation or chemical disinhibition, is associated with increases in respiratory activity observed via diaphragmatic electromyogram recordings. The present experiments address the potential for PPN involvement in the regulation of the reflex diaphragmatic responses to muscle contraction in chloralose-urethane anesthetized rats. Diaphragmatic responses to unilateral static hindlimb muscle contraction, evoked via electrical stimulation of the tibial nerve, were recorded before and subsequent to bilateral microinjections of a synaptic blockade agent (CoCl2) into the PPN. The peak reflex increases in respiratory frequency (9.0 +/- 1.0 breaths/min) and minute integrated diaphragmatic electromyogram activity (14.6 +/- 3.3 units/min) were attenuated after microinjection of CoCl2 into the PPN (2.6 +/- 0.9 breaths/min and 4.6 +/- 2.1 units/min, respectively). Consistent diaphragmatic responses were observed in the subset of animals that were barodenervated. Control experiments suggest no effects of PPN synaptic blockade on the cardiovascular responses to muscle contraction. The results are discussed in terms of a potential role for the PPN in modulation of the reflex respiratory adjustments that accompany muscular activity.

In vivo electrophysiological responses of pedunculopontine neurons to static muscle contraction.

The pedunculopontine nucleus (PPN) has previously been implicated in central command regulation of the cardiorespiratory adjustments that accompany exercise. The current study was executed to begin to address the potential role of the PPN in the regulation of cardiorespiratory adjustments evoked by muscle contraction. Extracellular single-unit recording was employed to document the responses of PPN neurons during static muscle contraction. Sixty-four percent (20/31) of neurons sampled from the PPN responded to static muscle contraction with increases in firing rate. Furthermore, muscle contraction-responsive neurons in the PPN were unresponsive to brief periods of hypotension but were markedly activated during chemical disinhibition of the caudal hypothalamus. A separate sample of PPN neurons was found to be moderately activated during systemic hypoxia. Chemical disinhibition of the PPN was found to markedly increase respiratory drive. These findings suggest that the PPN may be involved in modulating respiratory adjustments that accompany muscle contraction and that PPN neurons may have the capacity to synthesize muscle reflex and central command influences.

Respiratory, cardiovascular, and metabolic adjustments to hypoxemia during sleep in piglets

The influence of sleep on ventilation, metabolic rate, cardiovascular function, and regional distribution of blood flow during hypoxemia (PaO2 of 45-50 mmHg (1 mmHg = 133.3 Pa)) was studied in piglets at 6 ± 1 and 34 ± 5 days (mean ± SD). Measurement of ventilation and metabolic rate was done in a metabolic chamber, and blood flow was measured using the microsphere technique. A subgroup of animals was instrumented for cardiac output measurement (dye-dilution technique) and continuous monitoring of the hemoglobin saturation in oxygen (SaO2) We found that although sleep did not influence the metabolic and cardiac output response to hypoxemia, it affected the ventilatory response as well as the brain and the respiratory muscle blood flows. During active sleep in the older animals, the ventilatory response to hypoxemia was smaller than in the other two states; marked drops in SaO2 occurred with changes in the breathing pattern; and that state was associated with the highest rate of brain blood flow. As well, age affected the ventilatory and metabolic response, but not the cardiovascular response to hypoxemia. The age-dependent ventilatory changes with hypoxemia (smaller ventilatory response in the young than in the older animals) were related to the different levels of oxygen consumption. In summary, active sleep was responsible for all the sleep-dependent changes in the response to a moderate degree of hypoxemia.Key words: breathing pattern, metabolic rate, blood flow, microspheres, maturation.

Invited editorial on "Effect of arterial occlusion on responses of group III and IV afferents to dynamic exercise".

many of the cardiovascular and respiratory adjustments to exercise are mediated by activation of the sympathetic nervous system. This sympathetic activation has been attributed both to the central neural drive associated with the volitional component of exercise, termed “central command,” and to

Heart rate and respiratory adjustments during work of increasing intensity in Hinterwaelder and Zebu oxen

AbstractHeart rate, ventilation measurements and gas exchange were studied in seven Hinterwaelder (Bos taurus) (494 (s.e. 16) kg) and five zebu (Bos indicusj oxen (516 (s.e. 60) kg), while the animals were standing, walking and pulling different loads. During standing, the heart rate, respiration rate, ventilation volume per min, total carbon dioxide production, total oxygen consumption and oxygen consumption per heart beat were lower in the zebu group than in the Hinterwaelder group (P < 0·05). The higher values for the Hinterwaelder were probably due to their higher metabolic rate, because of their younger age, higher level of feeding and better quality diet. The adaptation of gas exchange to higher work loads was achieved mainly by higher ventilation volumes. The composition of the expired air changed minimally. At similar levels of draught power output, the total energy expenditure minus energy expenditure of walking of the zebu oxen was lower than that of the Hinterwaelder oxen (P < 0·02). On the other hand at similar levels of heat production, the heart rate and ventilation volume per min did not differ significantly between the two breeds (P > 0·05). In spite of the differences in environment, feeding level and draught efficiency, the physiological adaptations made by the two breeds in response to work were similar.

Cardiovascular and respiratory adjustments in normal volunteers during modified exercise tests in comparison to standard exercise tests.

Sixteen normal, non-smoking first year medical students underwent four standard exercise tests, while cardiovascular (heart rate and blood pressure) and pulmonary (respiratory rate, tidal volume and oxygen consumption) adjustments were being monitored. Maximal exercise level for all tests were defined following the Jones scale. No variation was noted in respiratory rate among the four exercise tests. The cycle ergometry (CE), hand ergometry (HE), and treadmill (TM) exercise tests produced progressive increases of the various parameters as expected, although target maximal heart rates were not reached in most cases secondary to muscle fatigue. The step test (ST) approximated the physiological parameter changes noted in these three tests during the early stages of exercise, but levelled off after 3 minutes, probably due to lack of incremental load. The ST took the longest time to reach maximal level of exercise parameters, and recorded the lowest tidal volume increase. The same subjects underwent a modified step test (MST1) by adding 1 kg sandbags every 3 min to backpacks worn by the subjects, to provide incremental load. This modification provided a slight increase in the parameters measured, but still plateaued after 3 min. Another set of 18 normal, non-smoking medical students underwent bicycle ergometry and two other modified exercise tests. The modified step test two (MST2) was similar to our initial MST1, except that the sandbags added every 3 min were not fixed at 1 kg but were also incremental (1, 2, 3 and 4 kg). The other test (Ramp test or RT) required the subjects to walk up and down a ramp, which entailed not only the addition of incremental weights of sandbags every 3 min, but also increasing the elevation of the ramp at each stage. Data analysis showed that these two tests showed almost similar changes in cardiovascular and respiratory adjustments in the subjects, compared to the standard bicycle ergometry. These pilot studies showed that low-cost modified step tests may be utilized to approximate the expensive standard treadmill and bicycle exercise tests. More studies on larger populations have to be done to validate these results.

Respiratory adjustments in unacclimatised horses exercised under hot, humid conditions

SummaryThe purpose of this study was to investigate the effect of a hot and humid environment on the pattern of breathing and the gas exchange in heavily exercising horses. Five healthy fit Standardbred horses were investigated twice at 8 day intervals, once in temperate conditions (TC) (ambient temperature: 15°C; relative humidity: 55%) and once in hot and humid conditions (HHC) (ambient temperature: 30°C; relative humidity: 75%). The standardised treadmill exercise test consisted of 8 min warm‐up and 8 min exercise (1 min at 1.7, 4, 7, 8, 9 and 10 m/s and 2 min at 4 m/s with a 6% slope). Running in HHC induced a significant decrease in peak expired minute volume (V̇E), oxygen uptake (V̇O2), V̇CO2and oxygen pulse, while RQ remained unchanged and PACO2increased. The changes in skin temperature (ST), i.e. the difference between ST at rest and at 10 m/s, was dramatically higher in HHC. The test induced changes, i.e. the differences between the values before and after the test, in Cortisol, β‐endorphins and plasma lactate (LA) values after the test were significantly higher. This study showed that performing a strenuous exercise in hot, humid conditions in unacclimatised horses induced a reduction of the aerobic capacity, i.e. decrease of the V̇O2and increase of LA production. A relative hypoventilation could be partly responsible for this observation, but all the steps of the oxygen transport from the pulmonary ventilation to the muscle metabolism could also potentially be impaired in such conditions.

Prostaglandin synthesis blockade by ketoprofen attenuates respiratory and cardiovascular responses to static handgrip

We investigated the effects of prostaglandin synthesis blockade on the changes in breathing pattern, mean blood pressure (MBP), and heart rate (HR) elicited by 3 min of static handgrip at 30% of the maximum voluntary contraction in 12 healthy volunteers. Before each handgrip trial, subjects were treated with intravenous administration of either saline placebo (control) or 1 mg/kg of ketoprofen. Muscle tension and integrated electromyographic activity of exercising muscles remained fairly constant during each trial. In agreement with our earlier findings, during control handgrip minute ventilation progressively increased (P < 0.01) due to a rise in tidal volume and, to a lesser extent, in respiratory frequency. Mean inspiratory flow, MBP, and HR also increased (P < 0.01). End-tidal PCO2 decreased (P < 0.05) during the late phases of control handgrip bouts. Ketoprofen administration reduced serum thromboxane B2 levels (from 57.5 +/- 7.0 to 1.6 +/- 0.4 pg/ml; P < 0.01) and significantly attenuated mean increases in minute ventilation (40.25 +/- 0.60%), tidal volume (37.78 +/- 7.48%), respiratory frequency (55.94 +/- 17.92%), inspiratory flow (42.66 +/- 5.11%), MBP (22.33 +/- 6.82%), and HR (11.04 +/- 2.75%) during the 3rd min of handgrip. End-tidal PCO2 remained close to normocapnic levels. In agreement with previous animal investigations, the present results show that arachidonic acid metabolites are involved in the regulation of the cardiovascular responses to static efforts in humans, possibly through a stimulatory action on muscle receptors. Furthermore, they provide the first experimental evidence that products of the cyclooxygenase metabolic pathway play a role in the mediation of the respiratory adjustments elicited by this form of exercise.

Photosynthetic Response to Light and Nutrients in Sun-Tolerant and Shade-Tolerant Rainforest Trees. II. Leaf Gas Exchange and Component Processes of Photosynthesis

Species with contrasting shade tolerance were grown under three light by two nutrient treatments. Gas exchange by intact leaves, leaf disk O2 evolution and chlorophyll fluorescence were measured. In shade-tolerant evergreen species (Argyrodendron sp., A. trifoliolatum and Flindersia brayleyana) photosynthetic activity of seedlings in air at light saturation (A) was lower under weak (30 pmol quanta m-2 day-1 ), compared with medium (130) or strong light (535). In Toona australis, a shade-intolerant and deciduous tree, A was reduced 44% from strong to weak light treatment on high nutrients (71 mg N L-1 nutrient solution). Nevertheless, nitrogen-use efficiency for leaf photosynthesis was highest in Toona under all growing conditions and, with higher specific leaf area, probably contributes towards fast occupancy of sites which underlies early succession in this species. All species made photosynthetic and respiratory adjustments from strong to medium to weak light, which resulted in a lower light compensation point (Q0). Such adjustments were accentuated by low nutrient supply (1.0 mg N L-1 nutrient solution) and were especially pronounced for shade-intolerant Toona. Reduced Q0 in Toona was accompanied by lower A and light saturation point (QA). Both species of Argyrodendron showed no decrease in QA despite reduction in Q0 under weak light.Contrary to expectation, photosynthetic responses to light × nutrient treatments did not correlate with degree of shade tolerance accorded each species by rainforest ecologists.

Rheological modelling of physiological variables during temperature variations at rest

The evolution with time of cardio-respiratory variables, blood pressure and body temperature has been studied on six males, resting in semi-nude conditions during short (30 min) cold stress exposure (0 degree C) and during passive recovery (60 min) at 20 degrees C. Passive cold exposure does not induce a change in HR but increases VO2, VCO2, Ve and core temperature Tre, whereas peripheral temperature is significantly lowered. The kinetic evolution of the studied variables was investigated using a Kelvin-Voigt rheological model. The results suggest that the human body, and by extension the measured physiological variables of its functioning, does not react as a perfect viscoelastic system. Cold exposure induces a more rapid adaptation for heart rate, blood pressure and skin temperatures than that observed during the rewarming period (20 degrees C), whereas respiratory adjustments show an opposite evolution. During the cooling period of the experiment the adaptative mechanisms, taking effect to preserve core homeothermy and to obtain a higher oxygen supply, increase the energy loss of the body.

A stage in glycolysis controls the metabolic adjustments of vertebrate rod photoreceptors upon illumination

The factors affecting the metabolic adjustments of toad rod photoreceptors were studied by monitoring the oxygen utilization of excised retinas and by measuring rod outer segment ATP and GTP concentrations. Respiratory adjustments upon illumination were observed when glucose or fructose was provided in the perfusate, but not when a glycolytic inhibitor was added to the perfusate containing glucose and pyruvate, or when a substrate beyond glycolysis or from a later stage of glycolysis was substituted for glucose. The amplitudes of the respiratory adjustments to illumination were dependent on the concentration of glucose in the perfusate. The ATP and GTP concentration changes were dependent on respiratory adjustments, including glycolytic effects, and on the levels of illumination. The data suggest a control point within glycolysis for light-induced adjustments of respiration, possibly at phosphofructokinase.

Heart Rate, Blood Pressure, Cardiac Output, and Total Peripheral Resistance of Single Comb White Leghorn Hens During an Acute Exposure to 35 C Ambient Temperature

Two experiments were undertaken to determine selected cardiovascular responses of laying hens to a thermal challenge at 35 C ambient temperature. In the first, six Single Comb White Leghorn (SCWL) hens were exposed to 35 C and changes in systolic and diastolic blood pressure, heart rate, respiratory rate, and rectal temperatures were determined. In the second, seven SCWL hens were exposed to 35 C and changes in cardiac output, total peripheral resistance, blood pressure, heart rate, respiratory rate, and rectal temperature were monitored. In the first experiment heart rate and blood pressure decreased. In the second experiment there was a 58% increase in cardiac output and a 50% decrease in total peripheral resistance accompanied by a 9% decrease in mean blood pressure. Changes in cardiovascular tone preceeded respiratory adjustments during acute heat challenges. This may represent one of the most efficient means of heat dissipation for the bird.

Right heart pressures and blood-gas tensions in ponies during exercise and laryngeal hemiplegia.

Right atrial, right ventricular, and pulmonary artery pressures, along with change in pleural pressure, were determined with catheter-tipped micromanometers in two groups of ponies at rest, as well as during moderate (trot; heart rate = 180 beats . min-1) and severe (gallop; heart rate = 220 beats . min-1) exercise performed on a treadmill. Group A (n = 8) ponies served as controls, and group B ponies (n = 6) had laryngeal hemiplegia (LH) induced by sectioning the left recurrent laryngeal nerve 20-29 days before the study. It was observed that LH ponies could not gallop for more than 45-90 s. With both levels of exertion, pressures in the right atrium, right ventricle, and pulmonary artery increased very significantly in normal ponies. The change in pleural pressure of galloping ponies was 30.4 +/- 2.9 cmH2O, and the respiratory (and stride) frequency was 138 +/- 4 breaths . min-1. During severe exercise in normal ponies, the systolic, mean, and diastolic pressures in the pulmonary artery were 107 +/- 7, 63.5 +/- 4.2, and 46 +/- 4 mmHg, despite the fact that no alveolar hypoxia could be detected. In LH ponies pulmonary artery pressures rose to levels observed in normal ponies, but during galloping, the change in pleural pressure (delta Ppl) (92 +/- 6 cmH2O) was three times that in normal ponies, and there was no synchronization of respiratory (86 +/- 6 breaths . min-1) frequency to stride frequency (142 +/- 3 strides . min-1). Despite these respiratory adjustments (decreased frequency and increased delta Ppl), arterial PO2 decreased and arterial PCO2 increased in galloping LH ponies.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory adjustments of the unanaesthetized chicken, Gallus domesticus, to elevated metabolism elicited by 2,4-dinitrophenol or cold exposure

1. 1. The effects of pharmacologically elevated metabolism on ventilation, gaseous exchange and blood gases were studied in spontaneously breathing unanaesthetized decerebrate chickens using 2,4-dinitrophenol (DNP) injected intravenously in successive single doses of 2.5–5.0 mg/kg. These responses were compared with the cardiorespiratory adjustments to elevated metabolism evoked by shivering in conscious birds. 2. 2. Oxygen consumption increased with cumulative amounts of DNP, reaching 275 ± 30% of control values at the maximum tolerated dose of 10–15 mg/kg. 3. 3. Increases in ventilation matched the changes in oxygen consumption via increases in both breathing frequency and tidal volume. Arterial blood gases and pH remained unchanged. 4. 4. Exposure to cold ( T a = 2 ± 2° C) caused oxygen consumption to increase to 185 ± 21% of control values. Respiratory and cardiovascular adjustments were similar to those evoked by DNP and were comparable to those produced by low intensity treadmill exercise (cf. Gleeson and Brackenbury, 1984).

Respiratory, cardiovascular, and metabolic adjustments to exercise in the Hereford calf

Six Hereford steers were studied before, during, and after short exercise bouts on a motor-driven treadmill (3 degrees incline) at four speeds (1.0, 1.4, 1.8, and 2.2 m X s-1). Oxygen consumption (MO2) and carbon dioxide production (MCO2) were measured by collecting the expired gas. Arterial and mixed venous blood samples were obtained simultaneously from indwelling catheters in the aorta and pulmonary artery. A 10-fold increase was observed in MO2 and MCO2 at the highest work load. Minute ventilation increased proportionately less than MO2 and MCO2 with increasing work loads, but alveolar ventilation was found to increase in proportion to both MO2 and MCO2. The highest work load produced a threefold increase in cardiac output primarily as a result of increased heart rate. A 10-fold increase in lactate and a 63% increase in serum potassium concentration were observed at the highest work load. Plasma cortisol levels were highest at 10 min postexercise and reached levels of seven times the resting values following exercise at the highest speed. The responses to exercise in the calf are qualitatively similar to those observed in other species, but quantitative differences exist in some cardiovascular and metabolic responses which may limit this animal's ability to perform strenuous exercise.

Cardiac, respiratory and metabolic changes during static exercise and voluntary heart rate acceleration

Various ventilatory and metabolic parameters were monitored in 12 subjects while they performed each of three tasks: Voluntary cardiac acceleration with the aid of continuous heart rate feedback; a static hand-grip exercise at 1 3 maximum voluntary contraction; and a combined task involving both voluntary acceleration and exercise. Task order was counterbalanced across subjects and there were six 30 sec trials of each task. While reliable cardiac accelerations were recorded throughout, they were substantially greater with the combined task. This confirmed previous findings attesting that individuals can voluntarily elevate heart rate above levels induced by standard physical loads. However, the pattern of results for oxygen consumption and carbon dioxide production, with the most substantial increase in both also occurring for combined voluntary acceleration and exercise, suggested that the cardiac elevations superimposed on exercise levels were largely non-specific, i.e. they involved additional energy expenditure. Respiration volume increased during the performance of all three tasks, with the greatest increase again occurring in the combined task. The precise respiratory adjustments, in terms of rate and tidal volume, varied subtly among tasks; while all three tasks produced a rise in respiration rate, only the combined task increased tidal volume.

Respiratory and circulatory control during sleep.

A survey of the literature on a large number of vertebrate animals shows that sleep is associated with profound cardiovascular and respiratory adjustments which are very similar in each species. A hypothesis is advanced that these adjustments are 'goal directed' by neural structures in the brainstem, to ensure an adequate O2 and CO2 transport to and from the brain whilst at the same time reducing energy cost. During synchronised sleep there is a vagal bradycardia leading to reduced cardiac output and a fall in blood pressure; despite this cerebral blood flow increases. During desynchronized sleep there is a tonic fall in blood pressure and heart rate resulting from a unique repatterning of sympathetic discharge, that to heart, kidney, splanchnic and pelvic vascular beds decreasing whilst that to skeletal muscle increasing; cerebral blood flow shows a further increase. This differential pattern is probably initiated by neurones located in the caudal raphe nucleus obscurus. Phasic increases in blood pressure and heart rate also occur during desynchronized sleep mainly as a consequence of increases in sympathetic activity. Ventilation decreases during synchronized sleep accompanied by an increase in partial pressure of arterial CO2, which vasodilates cerebral blood vessels, indicating that the influence of CO2 on the level of ventilation has changed. During desynchronized sleep ventilation increases and becomes very irregular but the partial pressure of O2 and CO2 in arterial blood is little changed from wakefulness. Control of respiration is shifted to a central generator which apparently is different to the automatic/metabolic one which is normally dominant during wakefulness. Reflex control of the circulation and respiration is mainly governed by peripheral chemoreceptors, the threshold of most other afferent inputs being significantly raised during sleep.