Altered Breathing Pattern Research Articles

Maternal dietary tryptophan deficiency alters cardiorespiratory control in rat pups

Malnutrition during pregnancy adversely affects postnatal forebrain development; its effect upon brain stem development is less certain. To evaluate the role of tryptophan [critical for serotonin (5-HT) synthesis] on brain stem 5-HT and the development of cardiorespiratory function, we fed dams a diet ∼45% deficient in tryptophan during gestation and early postnatal life and studied cardiorespiratory variables in the developing pups. Deficient pups were of normal weight at postnatal day (P)5 but weighed less than control pups at P15 and P25 (P < 0.001) and had lower body temperatures at P15 (P < 0.001) and P25 (P < 0.05; females only). Oxygen consumption (Vo(2)) was unaffected. At P15, deficient pups had an altered breathing pattern and slower heart rates. At P25, they had significantly lower ventilation (Ve) and Ve-to-Vo(2) ratios in both air and 7% CO(2). The ventilatory response to CO(2) (% increase in Ve/Vo(2)) was significantly increased at P5 (males) and reduced at P15 and P25 (males and females). Deficient pups had 41-56% less medullary 5-HT (P < 0.01) compared with control pups, without a difference in 5-HT neuronal number. These data indicate important interactions between nutrition, brain stem physiology, and age that are potentially relevant to understanding 5-HT deficiency in the sudden infant death syndrome.

The Effect ofIn UteroCigarette Smoke Exposure on Development of Respiratory Control: A Review

Maternal cigarette smoking is the most modifiable risk factor for sudden infant death syndrome. Although the mechanism underlying the association between maternal smoking and sudden infant death syndrome is unknown, the effect of in utero cigarette smoke exposure on respiratory control development is speculated as the important causative mechanism. In human, several studies have linked maternal smoking and alterations in breathing pattern, ventilatory, and arousal responses in infants during the early postnatal age. Cigarette contains many compounds, but nicotine has been identified as the main culprit underlying changes in respiratory control. Further investigations in animal models have demonstrated that perinatal nicotine exposure results in alteration in baseline ventilation, ventilatory response to hypoxia, arousals, and autoresuscitation processes in developing animals. The mechanisms underlying the effect of nicotine exposure on respiratory control may be related to modulation of neurotransmitters and signal transductions mediating ventilatory control and arousal responses. Findings from these studies will help to understand how perinatal cigarette smoke exposure interferes with respiratory control development, and may lead to more effective preventive strategies and therapeutic intervention for this significant health problem.

Causes of Breathing Inefficiency During Exercise in Heart Failure

Background Patients with heart failure (HF) develop abnormal pulmonary gas exchange; specifically, they have abnormal ventilation relative to metabolic demand (ventilatory efficiency/minute ventilation in relation to carbon dioxide production [V E/VCO 2]) during exercise. The purpose of this investigation was to examine the factors that underlie the abnormal breathing efficiency in this population. Methods and Results Fourteen controls and 33 moderate-severe HF patients, ages 52 ± 12 and 54 ± 8 years, respectively, performed submaximal exercise (∼65% of maximum) on a cycle ergometer. Gas exchange and blood gas measurements were made at rest and during exercise. Submaximal exercise data were used to quantify the influence of hyperventilation (PaCO 2) and dead space ventilation (V D) on V E/VCO 2. The V E/VCO 2 relationship was lower in controls (30 ± 4) than HF (45 ± 9, P < .01). This was the result of hyperventilation (lower PaCO 2) and higher V D/V T that contributed 40% and 47%, respectively, to the increased V E/VCO 2 ( P < .01). The elevated V D/V T in the HF patients was the result of a tachypneic breathing pattern (lower V T, 1086 ± 366 versus 2003 ± 504 mL, P < .01) in the presence of a normal V D (11.5 ± 4.0 versus 11.9 ± 5.7 L/min, P = .095). Conclusions The abnormal ventilation in relation to metabolic demand in HF patients during exercise was due primarily to alterations in breathing pattern (reduced V T) and excessive hyperventilation.

Breathing Efficiency in Systolic Heart Failure: Impact of Hyperventilation and Dead Space

BackgroundPatients with heart failure (HF) often develop pulmonary system abnormalities. Specifically, an abnormal ventilation relative to metabolic demand (VE/VCO2, ventilatory efficiency) during exercise has been shown to be an important marker of disease severity and prognosis. The purpose of this investigation was to focus on the factors that underlie the abnormal breathing efficiency in this population.Methods14 controls (10 male) and 40 (36 male) mod‐severe HF patients, age 52±12 and 56±8 yrs, respectively, performed graded exercise on a cycle ergometer. Gas exchange and blood gas measurements were made during submaximal exercise (~65% peak VO2) and used to quantify the influence of hyperventilation (PaCO2) and dead space ventilation (VD) on VE/VCO2.ResultsThe VE/VCO2 ratio was lower in controls (30±4) than in HF (45±9, p&lt;0.001) due to a lower PaCO2 and higher VD/VT that contributed an estimated 29% and 71%, respectively, to the increased VE/VCO2 (p&lt;0.05). The elevated VD/VT in HF was in turn the result of a tachypneic breathing pattern (lower VT, 877±306 vs 2003±504ml, p&lt;0.01) in the presence of a relatively normal VD (9.6±3.8 vs 11.9±5.7 L/min, p=0.094).ConclusionThe abnormal ventilation in relation to metabolic demand in HF during exercise is predominantly due to alterations in breathing pattern, rather than hyperventilation or changes in ventilation/perfusion relationships. HL71478

Disnea de esfuerzo, deterioro del patrón ventilatorio y mala tolerancia al ejercicio: ¿signos precoces de insuficiencia respiratoria?

Exertional dyspnea (ED) is common among smokers despite a normal spirometry. Objectives This study aimed to determine whether exercise testing, overbreathing and altered breathing pattern can reflect early respiratory impairment. Material and method Twenty-four active ED male smokers aged 33–60 years, with no background of muscular, cardiac or respiratory disease, were compared to 31 healthy smokers (with no ED). Spirometry, plethysmography, ventilatory pattern and arterial blood gases were assessed in both groups and dyspnea was estimated using a Borg scale at every 30W/3 min step of incremental maximal exercise, starting with 40 W for 10 min. Results Spirometry data was normal in both groups. Compared to healthy subjects, the respiratory pattern was significantly (p<0.001) more rapid and shallow with smaller tidal volume (VT) (p<0.001) and less alveolar ventilation ( V ˙ A / V ˙ E ) and PaO 2 while ventilation ( V ˙ E ), the ratio V ˙ E /MVV, ventilatory frequency (fB), dead space ventilation (VD), lactic acidemia, and cardiac frequency (fC) were significantly higher (p<0.01) in the ED group. The significant differences (p<0.05) observed at rest were amplified during exercise and V ˙ O 2 pico and maximal power load were 30% lower (p<0.001) in ED subjects. Conclusions Apparently healthy subjects, whose spirometry are normal, complain of exertional dyspnea associated with a combination of adverse effects of: increased central ventilatory demand, overbreathing, impairments of ventilatory pattern, hypoventilation, and severe reduction of the maximal levels of exercise. These changes are not often explored, although they are potentially susceptible to correction corrected with sophisticated respiratory physiotherapy and exercise training.

A influência de duas frações inspiradas de oxigênio no padrão respiratório de pacientes sob desmame ventilatório

An inspired oxygen fraction (FiO2) of 40% is often used for weaning patients, but lower FiO2 values are also recommended, if arterial oxygen pressure (PaO2)/ FiO2 >150-200 mmHg. This study aimed to compare respiratory variables and vital data values recorded during use of sufficient FiO2 (ideal) to maintain peripheral oxygen saturation at 92% with values recorded during use of FiO2 established at 40% (baseline) in weaning patients. Prospective cross-over study. Respiratory variables (respiratory frequency, tidal volume, occlusion pressure, inspiratory time/total time ratio) and vital data (blood pressure and heart rate) were collected sequentially at 30 and 60 minutes with baseline FiO2, followed by ideal FiO2. These were compared to a generalized linear model for repeated measurements. Comparisons between baseline and ideal FiO2 values, and arterial blood gases were evaluated by the Student's t or Wilcoxon tests. In 30 adult patients the median of ideal FiO2 was 25% (IQ25%-75% 23-28). This was significantly lower than baseline FiO2 (40%) (p< 0.001). No significant difference was found in the PaO2/ FiO2 ratio between baseline FiO2 (269±53) and ideal FiO2 (268±47). Tidal volume was significantly lower during use of ideal FiO2 (p=0.003) and blood pressure was significantly higher during use of baseline FiO2 (p=0.041), but there was no clinical significance. The remaining variables were not affected by reduction in FiO2. The ideal FiO2 did not influence remaining variables. These results suggest that FiO2 levels sufficient to ensure a SpO2>92% did not alter breathing patterns or trigger clinical changes in weaning patients.

Reviewer’s comments concerning “Altered breathing patterns during lumbopelvic motor control tests in chronic low back pain: a case–control study” (J. Nijs et al., ESJO-D-08-00264 R2)

Reviewer’s comments concerning “Altered breathing patterns during lumbopelvic motor control tests in chronic low back pain: a case–control study” (J. Nijs et al., ESJO-D-08-00264 R2)

Altered breathing patterns during lumbopelvic motor control tests in chronic low back pain: a case-control study.

The objective of the study was to evaluate the breathing pattern in patients with chronic non-specific low back pain (LBP) and in healthy subjects, both at rest and during motor control tests. Ten healthy subjects and ten patients with chronic LBP participated at this case-control study. The breathing pattern was evaluated at rest (standing and supine position during both relaxed breathing and deep breathing) and while performing clinical motor control tests, i.e. bent knee fall out and active straight leg raise. A blinded observer analyzed the breathing pattern of the participants using visual inspection and manual palpation. Costo-diaphragmatic breathing was considered as optimal breathing pattern. Subjects filled in visual analog scales for the assessment of pain intensity during the tests. At rest, no significant differences were found between the breathing pattern of patients and healthy subjects (P > 0.05). In contrast, significantly more altered breathing patterns were observed in chronic LBP-patients during motor control tests (P = 0.01). Changes in breathing pattern during motor control tests were not related to pain severity (P > 0.01), but were related to motor control dysfunction (P = 0.01).

Lung Volume, Breathing Pattern and Ventilation Inhomogeneity in Preterm and Term Infants

BackgroundMorphological changes in preterm infants with bronchopulmonary dysplasia (BPD) have functional consequences on lung volume, ventilation inhomogeneity and respiratory mechanics. Although some studies have shown lower lung volumes and increased ventilation inhomogeneity in BPD infants, conflicting results exist possibly due to differences in sedation and measurement techniques.Methodology/Principal FindingsWe studied 127 infants with BPD, 58 preterm infants without BPD and 239 healthy term-born infants, at a matched post-conceptional age of 44 weeks during quiet natural sleep according to ATS/ERS standards. Lung function parameters measured were functional residual capacity (FRC) and ventilation inhomogeneity by multiple breath washout as well as tidal breathing parameters. Preterm infants with BPD had only marginally lower FRC (21.4 mL/kg) than preterm infants without BPD (23.4 mL/kg) and term-born infants (22.6 mL/kg), though there was no trend with disease severity. They also showed higher respiratory rates and lower ratios of time to peak expiratory flow and expiratory time (t PTEF/t E) than healthy preterm and term controls. These changes were related to disease severity. No differences were found for ventilation inhomogeneity.ConclusionsOur results suggest that preterm infants with BPD have a high capacity to maintain functional lung volume during natural sleep. The alterations in breathing pattern with disease severity may reflect presence of adaptive mechanisms to cope with the disease process.

Prenatal nicotine exposure and development of nicotinic and fast amino acid-mediated neurotransmission in the control of breathing

There is mounting evidence that neonatal animals exposed to nicotine in the prenatal period exhibit a variety of anatomic and functional abnormalities that adversely affect their respiratory and cardiovascular control systems, but how nicotine causes these developmental alterations is unknown. The principle that guides our work is that PNE impairs the ability of nicotinic acetylcholine receptors (nAChRs) to modulate the pre-synaptic release of both inhibitory (particularly GABA) and excitatory (glutamate) neurotransmitters, leading to marked alterations in the density and/or function of receptors on the (post-synaptic) membrane of respiratory neurons. Such changes could lead to impaired ventilatory responses to sensory afferent stimulation, and altered breathing patterns, including central apneic events. In this brief review we summarize the work that lead to the development of this hypothesis, and introduce some new data that support and extend it.

Evaluation of Breathing Pattern: Comparison of a Manual Assessment of Respiratory Motion (MARM) and Respiratory Induction Plethysmography

Altered breathing pattern is an aspect of dysfunctional breathing but few standardised techniques exist to evaluate it. This study investigates a technique for evaluating and quantifying breathing pattern, called the Manual Assessment of Respiratory Motion (MARM) and compares it to measures performed with Respiratory Induction Plethysmography (RIP). About 12 subjects altered their breathing and posture while 2 examiners assessed their breathing using the MARM. Simultaneous measurements with RIP were taken. Inter-examiner agreement and agreement between MARM and RIP were assessed. The ability of the measurement methods to differentiate between diverse breathing and postural patterns was compared. High levels of agreement between examiners were found with the MARM for measures of the upper rib cage relative to lower rib cage/abdomen motion during breathing but not for measures of volume. The measures of upper rib cage dominance during breathing correlated with similar measures obtained from RIP. Both RIP and MARM measures methods were able to differentiate between abdominal and thoracic breathing patterns, but only MARM was able to differentiate between breathing changes occurring as result of slumped versus erect sitting posture. This study suggests that the MARM is a reliable clinical tool for assessing breathing pattern.

Investigating the Claims of Konstantin Buteyko, M.D., Ph.D.: The Relationship of Breath Holding Time to End Tidal CO2and Other Proposed Measures of Dysfunctional Breathing

Konstantin Buteyko, M.D., Ph.D., claimed that breath holding time (BHT) can be used to detect chronic hyperventilation and that BHT predicts alveolar CO(2) (Pa(CO(2))) according to his patented mathematical formula. The Buteyko Breathing Technique (BBT) is believed to correct chronic hyperventilation as evidenced by increased BHT. In this study, we test Buteyko's claims and explore the relationship between BHT and end-tidal carbon dioxide (ETCO(2)) as well as measures of dysfunctional breathing (DB) including the Nijmegen questionnaire, the Self Evaluation of Breathing Questionnaire, and thoracic dominant breathing pattern. Eighty-three (83) adults healthy or suspected of having dysfunctional breathing, 29 with abnormal spirometry readings, 54 with normal spirometry. BHT, performed according to BBT protocols, was measured along with ETCO(2) and other measures of DB including the Nijmegen questionnaire, and manual assessment of respiratory motion, a palpatory technique for measuring thoraco-abdominal balance during breathing. Correlations between measures of DB were made in the whole sample and also in subgroups with normal or abnormal spirometry. DB measures were compared in normal and abnormal spirometry groups. The results revealed a negative correlation between BHT and ETCO(2) (r= -0.241, p<0.05), directly opposite to Buteyko's claims. BHT was significantly shorter in people with abnormal spirometry (FEV(1) or FVC<15% below predicted), with no difference in ETCO(2) levels between the abnormal and normal spirometry groups. In the abnormal spirometry group, lower BHT was found to correlate with a thoracic dominant breathing pattern. (r= -0.408, p<0.028). Although BHT does not predict resting ETCO(2), it does correlate with breathing pattern in subjects with abnormal spirometry. It is proposed that altered breathing pattern could contribute to breathing symptoms such as dyspnea and that breathing therapies such as BBT might influence symptoms by improving the efficiency of the biomechanics of breathing.

Chronic hypoxic hypercapnia modifies in vivo and in vitro ventilatory chemoreflexes in the cane toad

Previous studies have shown that exposure to chronic hypoxia (CH) and chronic hypercapnia (CHC) alone have opposite effects on central respiratory-related pH/CO(2) chemosensitivity in the cane toad (Bufo marinus). This study examined the effects of chronic hypoxic hypercapnia (CHH) on central pH/CO(2) chemosensitivity. Cane toads were maintained at 10% O(2) and 3.5% CO(2) for 10 days. Changes in central pH/CO(2)-sensitive fictive breathing were measured using in vitro brainstem-spinal cord preparations. Whole animal experiments examined the effects of CHH on in vivo ventilatory responses. In vitro, CHH augmented fictive breathing frequency but attenuated the integrated fictive breath area such that total fictive breathing was not altered. The effects on frequency were mediated by changes in the number of episodes/min rather than breaths/episode. In vivo, CHH blunted the ventilatory response to severe hypoxia and moderate hypercapnia. The results indicate that CHH alters breathing pattern in response to central chemoreceptor stimulation in vitro and modifies in vivo ventilatory chemoreflexes.

Self-Reported Snoring, Maternal Obesity and Neck Circumference as Risk Factors for Pregnancy-Induced Hypertension and Preeclampsia

Background: Physical and hormonal changes during pregnancy alter breathing patterns of pregnant women. It is possible that occult disordered breathing during sleep may be a risk factor for the development of pregnancy-induced hypertension (PIH) and preeclampsia. Objective: Our aim was to determine the incidence of self-reported snoring in pregnant women, and to investigate the relationship of snoring, obesity and neck circumference to PIH and preeclampsia. Methods: 469 pregnant women and 208 age-matched nonpregnant women were included in the study. Both groups were asked to complete a questionnaire. Maternal complications were retrieved from the medical records. Results: Habitual snoring was reported from 1.9% of nonpregnant women, 2.5% of pregnant women prior to pregnancy and 11.9% of those same women during the third trimester of pregnancy (p < 0.001). Age, smoking during pregnancy, and weight before delivery were independent risk factors for habitual snoring in pregnancy. PIH and preeclampsia developed in 20 and 10.9% of pregnant women with habitual snoring, as compared to 11 and 5.8% of non-snoring pregnant women (p = 0.045, p = 0.125, p = 0.415), respectively. In women who developed preeclampsia, weight before pregnancy, weight before delivery and neck circumference were significantly higher in univariate analysis. Neck circumference was an independent risk factor for PIH and preeclampsia according to logistic regression analysis. Conclusion: The incidence of snoring is significantly higher in pregnant women than in nonpregnant women. Snoring may indicate a risk of PIH. Neck circumference was an independent risk factor for both PIH and preeclampsia.

Exercise Capacity, Breathing Pattern, and Gas Exchange During Exercise for Patients with Isolated Diastolic Dysfunction

Left ventricular diastolic dysfunction (DiaD) is as common as left ventricular systolic dysfunction. Whether these causes of heart failure lead to similar breathing pattern and gas exchange responses to exercise remains unclear. Participants (control subjects [n = 47], systolic dysfunction [n = 46], and DiaD [n = 40]) underwent resting echocardiograms and cardiopulmonary exercise testing. Patients demonstrated lower peak oxygen consumption and tidal volume than control subjects (P < .05). Ventilation tended to be highest in DiaD. The submaximal ventilatory equivalent for carbon dioxide was highest in DiaD. Left atrial volume (all groups) was correlated with peak oxygen consumption (r = -0.38) whereas the ratio of early mitral inflow velocity to early mitral annular velocity was related to peak oxygen consumption (r = -0.36) and treadmill time (r = -0.35). Isolated DiaD is associated with altered breathing pattern and gas exchange similar to systolic dysfunction. Elevated left atrial volume, higher early mitral inflow velocity to early mitral annular velocity ratio, or both are predictive of exercise capacity and elevated ventilatory responses in patients with DiaD suggesting a role for dysfunctional ventricular relaxation.

Spinal cord injury in neonate rats alters respiratory neural output via supraspinal mechanisms

The primary cause of mortality in spinal cord injured patients is respiratory insufficiency. Upper cervical spinal cord injury (SCI) interrupts descending respiratory motor drive, altering ventilation. Alterations in breathing patterns after SCI are dependent on peripheral feedback mechanisms; however, it is not clear whether supraspinal plasticity also occurs. Alterations in respiratory frequency after SCI could suggest supraspinal plasticity since respiratory frequency is controlled at the brainstem level. We hypothesized that SCI may induce supraspinal respiratory plasticity in rats. Therefore, we examined the effect of C2 hemisection in neonate rats on the respiratory-like motor output of brainstem-spinal cord preparations. On postnatal day (P)0 or 1, a C2 hemisection surgery was performed under ketamine/xylazine and cold anesthesia. On P3, P4, or P5, rats (hemisected and littermate controls) were deeply anesthetized with halothane and brainstem-spinal cords removed. Respiratory-related activity was recorded from C4 ventral roots while the pH of the superfusate was changed (pH 7.2, 7.4 and 7.8). Respiratory-like frequency was significantly increased as pH was decreased in both hemisected (n=6) and controls (n=6) (p<0.001). The frequency of respiratory-like neural discharge was significantly reduced in hemisected rats compared to controls at all pH values (p=0.015). These data suggest that SCI does not alter the sensitivity to pH, but that supraspinal plasticity of the respiratory system occurs in neonate rats since the frequency of the in-vitro preparation was significantly altered. The mechanisms underlying this supraspinal respiratory plasticity after SCI remain unknown. This research was supported by NIH grant HD 31550

Das Flussolfaktometer nach Kobal im klinischen Einsatz für die subjektive und objektivierende Olfaktometrie

Is the flow-olfactometer OM2S suitable for subjective and objectifying screening of olfactory function, additional to its use for chemosensory evoked potentials? 53 normosmics were challenged prenasally and synchronously with inspiration by two short weak, moderate and strong hydrogen sulfide (H (2)S)- and phenylethyl alcohol (PEA)-stimuli. The subject pressed a button if there was an olfactory perception. The respiratory nasal pressure changes were recorded continuously via a differential pressure transducer. The alterations of breathing pattern during olfactory stimulation were calculated using a custom made LabView software. The interstimulus interval was at least 3 minutes, the respiration had to be regular. The detection-rate (79 - 98 %) was dependent on quality of odor and its concentration during stimulation. H (2)S-stimuli were detected more frequently than PEA-stimuli. The frequency of detection with simultaneous alteration of breathing pattern was independent of quality of odor and strength of odor concentration. 64 % of the subjects detected both weak H (2)S as well as changed synchronously their first poststimulatory breath. The H (2)S-detection threshold was estimated both by subjective data and by data of olfactory evoked respiration changes. The flow-olfactometer by Kobal is very well suitable for subjective and respiration-olfactometry, too.

Spinal Activation of Serotonin 1A Receptors Enhances Latent Respiratory Activity After Spinal Cord Injury

Background/Objective: Hemisection of the cervical spinal cord results in paralysis of the ipsilateral hemidiaphragm. Removal of sensory feedback through cervical dorsal rhizotomy activates latent respiratory motor pathways and restores hemidiaphragm function. Because systemic administration of serotonin 1A receptor (5HT1A) agonists reversed the altered breathing patterns after spinal cord injury (SCI), we predicted that 5HT1A receptor activation after SCI (C2) would activate latent crossed motor pathways. Furthermore, because 5HT1A receptors are heavily localized to dorsal horn neurons, we predicted that spinal administration of 5HT1A agonists should also activate latent motor pathways.Methods: Hemisection of the C2 spinal cord was performed 24 to 48 hours, 1 week, or 16 weeks before experimentation. Bilateral phrenic nerve activity was recorded in anesthetized, vagotomized, paralyzed Sprague-Dawley rats, and 8-OH-DPAT (5HT1A agonist) was applied to the dorsal aspect of the cervical spinal cord (C3-C7) or injected systemically.Results: Systemic administration of 8-OH-DPAT led to a significant increase in phrenic frequency and amplitude, whereas direct application to the spinal cord increased phrenic amplitude alone. Both1 systemic and spinal administration of 8-OH-DPAT consistently activated latent crossed phrenic activity. 8-OH-DPAT induced a greater respiratory response in spinal injured rats compared with controls.Conclusion: The increase in crossed phrenic output after application of 8-OH-DPAT to the spinal cord suqgests that dorsal horn inputs, respiratory and/or nonrespiratory, may inhibit phrenic motor output, especially after SCI. These findings support the idea that the administration of 5HT1A agonists may be a beneficial therapy in enhancing respiratory neural output in patients with SCI.

An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe

To avoid limitations associated with the use of single-breath and rebreathe methods for assessing the lung diffusing capacity for carbon monoxide (D(L)CO) during exercise, we developed an open-circuit technique. This method does not require rebreathing or alterations in breathing pattern and can be performed with little cognition on the part of the patient. To determine how this technique compared with the traditional rebreathe (D(L)CO,RB) method, we performed both the open-circuit (D(L)CO,OC) and the D(L)CO,RB methods at rest and during exercise (25, 50, and 75% of peak work) in 11 healthy subjects [mean age = 34 yr (SD 11)]. Both D(L)CO,OC and D(L)CO,RB increased linearly with cardiac output and external work. There was a good correlation between D(L)CO,OC and D(L)CO,RB for rest and exercise (mean of individual r2 = 0.88, overall r2 = 0.69, slope = 0.97). D(L)CO,OC and D(L)CO,RB were similar at rest and during exercise [e.g., rest = 27.2 (SD 5.8) vs. 29.3 (SD 5.2), and 75% peak work = 44.0 (SD 7.0) vs. 41.2 ml.min(-1).mmHg(-1) (SD 6.7) for D(L)CO,OC vs. D(L)CO,RB]. The coefficient of variation for repeat measurements of D(L)CO,OC was 7.9% at rest and averaged 3.9% during exercise. These data suggest that the D(L)CO,OC method is a reproducible, well-tolerated alternative for determining D(L)CO, particularly during exercise. The method is linearly associated with cardiac output, suggesting increased alveolar-capillary recruitment, and values were similar to the traditional rebreathe method.

Influence of prenatal nicotine exposure on postnatal development of breathing pattern.

To determine if prenatal nicotine exposure alters the postnatal development of the ventilatory pattern and the frequency and duration of apneas, we recorded respiratory airflow with head-out body plethysmography in awake neonates on postnatal days 1, 2, 6, 10, 14, and 18. Data from 12 nicotine-exposed animals were compared with data from 12 saline-exposed animals. Nicotine (6 mg/kg of nicotine tartrate per day) or saline exposure was induced by osmotic minipumps that were implanted subdermally on the fifth day of gestation in Sprague-Dawley Dams. Although both saline- and nicotine-exposed pups gained weight at the same rate throughout the studies, there were subtle differences in ventilatory indices between the two groups. Nicotine-exposed animals had a significantly higher breathing frequency on day 10, and a lower tidal volume on days 14 and 18. Although ventilation tended to be lower in the nicotine-exposed animals, the difference was not significant. There was a significantly higher frequency of apneas in the nicotine-exposed compared with the saline-exposed animals on postnatal days 1 and 2, but the apnea duration did not differ between the groups. No apneas were observed in any of the animals after the sixth postnatal day. Prenatal nicotine exposure is associated with a greater incidence of apneas on the first two postnatal days, and then an altered breathing pattern that manifests at a later stage of development.