Separate and combined effects of temperature and hypoxia on breathing pattern in the domestic fowl

Summary Minute ventilation (V _E), tidal volume (V _T), respiratory frequency (f) and clavicular air sac gas composition were measured in conscious domestic fowl breathing air and hypoxic gas mixtures at neutral (18±1°C) and raised (33±1°C) air temperatures. Increases inV _E caused by inhalation of 10%, 8% or 6.5% O₂ in N₂, respectively, were independent of temperature although at each level the absoluteV _E was ca. 21·min⁻¹ greater in the panting birds. Changes in respiratory pattern during hypoxia were markedly dependent on temperature. At 18°C almost all of the increasedV _E resulted from increasedf. At 33°C hypoxia led to a strong suppression off and increase inV _T. It is concluded that hyperthermia and hypoxia are additive and non-interactive in their effects on ventilatory drive, in agreement with previously reported effects of hypercapnia and physical exercise on breathing in panting fowl.     

Pulmonary ventilation and cardiac activity in hibernating and arousing golden-mantled ground squirrels (Spermophilus lateralis)

Pulmonary ventilation was assessed in the hibernating and arousing golden-mantled ground squirrel by plethysmography and end-tidal gas analysis. The heart rate and electrocardiogram were monitored simultaneously with ventilation. The hibernating squirrels displayed a periodic respiratory pattern characterized by a variable breathing frequency and tidal volume and often exhibited characteristics of Cheyne-Stokes respiration. Apneic periods averaging 8 to 9 min resulted in a low overall breathing frequency. Cardiac activity in the hibernating ground squirrel was characterized by arrhythmias which correlated with ventilation and by alterations in the electrocardiogram typically seen in hibernating animals. Arousal from hibernation was accompanied by: (i) a replacement of periodic by continuous ventilation, (ii) a 25-fold increase in V_E in the first hour which was accounted for by the increment in breathing frequency, and (iii) a marked decrease in the ratio of heart beats to breaths. The techniques developed in the present study will permit further quantitative investigations of pulmonary ventilation and its control in hibernating animals.     

Validation of Respiratory Inductance Plethysmography for Measuring Tidal Volume in Swine

Measuring tidal volume (V_T) in nonintubated swine or swine with leaking breathing circuits is challenging. The aim of this study was to validate respiratory inductance plethysmography (RIP) for measuring V_T in swine that are comparable in size to adult humans. To determine calibration curves, V_T and RIP readings were obtained from anesthetized swine (n = 8; weight, 46–50 kg) during positive-pressure (mechanical) ventilation and spontaneous breathing. For positive-pressure ventilation, 6 pigs were mechanically ventilated by using the pressure-control mode. The 2 pigs in the spontaneously breathing cohort each received a single intravenous bolus dose of propofol to abolish spontaneous breathing; V_T was measured during gradual return of their respiratory drive. A flow–volume sensor was placed between the proximal end of the endotracheal tube and breathing circuit for the recording of inspiratory and expiratory V_T. RIP readings were recorded by using 2 bands, which simultaneously measured ribcage and abdominal excursions. The data revealed that V_T was linearly correlated with the movements of both ribcage and abdomen as measured by using plethysmography over a large range of tidal volume (44 to 1065 mL). In addition, the intercept of the linear equation was small or even negative during spontaneous breathing but increased significantly (maximum, 145 mL, 59.2 ± 35.1 mL) during positive pressure ventilation. Our results indicate that V_T in swine can be calculated by using a simple univariate linear regression equation with RIP readings obtained during either mechanical ventilation or spontaneous breathing.Abbreviations: RIP, respiratory inductance plethysmography; V_T, tidal volumeIn animal care and research, the respiratory function of swine is widely assessed by measuring tidal volume (V_T).⁶ Although V_T is easy to measure in intubated pigs, it is difficult to measure in swine that are either nonintubated or have significant breathing circuit leakage^16,24. Using facemasks attached to minimally restrained swine is currently the method of choice for measuring V_T. This methodology has multiple limitations, including incomplete sealing between the pig''s face and the mask, which is difficult to adapt to these animals. A reliable, minimally invasive method for determining V_T in this species is needed.Respiratory inductance plethysmography (RIP)^11,15 is a viable alternative to measuring V_T. Using RIP, both ribcage and abdominal movements can be recorded. The amplitude changes of the ribcage and abdomen are linearly correlated to the size of the corresponding V_T in humans. This method has been validated in humans^1,13 and is widely used clinically in adults,^14,18 newborns and infants.^5,8 RIP has also been used on animals including sheep⁴ and dogs.¹⁷However, RIP has not yet been validated for use in swine that are comparable in size to adult humans. Considering the profound physiologic and anatomic differences in the respiratory system between swine and humans,^12,20 the validation of plethysmography for use in humans might not extrapolate readily to swine, which are one of the most commonly used animal models in biomedical research. Here we sought to validate the RIP method for calculating V_T in swine during both positive-pressure ventilation and spontaneous breathing.     

Correlated Variability in the Breathing Pattern and End-Expiratory Lung Volumes in Conscious Humans

In order to characterize the variability and correlation properties of spontaneous breathing in humans, the breathing pattern of 16 seated healthy subjects was studied during 40 min of quiet breathing using opto-electronic plethysmography, a contactless technology that measures total and compartmental chest wall volumes without interfering with the subjects breathing. From these signals, tidal volume (V_T), respiratory time (T_TOT) and the other breathing pattern parameters were computed breath-by-breath together with the end-expiratory total and compartmental (pulmonary rib cage and abdomen) chest wall volume changes. The correlation properties of these variables were quantified by detrended fluctuation analysis, computing the scaling exponentα. V_T, T_TOT and the other breathing pattern variables showed α values between 0.60 (for minute ventilation) to 0.71 (for respiratory rate), all significantly lower than the ones obtained for end-expiratory volumes, that ranged between 1.05 (for rib cage) and 1.13 (for abdomen) with no significant differences between compartments. The much stronger long-range correlations of the end expiratory volumes were interpreted by a neuromechanical network model consisting of five neuron groups in the brain respiratory center coupled with the mechanical properties of the respiratory system modeled as a simple Kelvin body. The model-based α for V_T is 0.57, similar to the experimental data. While the α for T_TOT was slightly lower than the experimental values, the model correctly predicted α for end-expiratory lung volumes (1.045). In conclusion, we propose that the correlations in the timing and amplitude of the physiological variables originate from the brain with the exception of end-expiratory lung volume, which shows the strongest correlations largely due to the contribution of the viscoelastic properties of the tissues. This cycle-by-cycle variability may have a significant impact on the functioning of adherent cells in the respiratory system.     

Ventilatory accommodation of oxygen demand and respiratory water loss in a large bird,the emu (Dromaius novaehollandiae), and a re-examination of ventilatory allometry for birds

Ventilation was studied in the emu, a large flightless bird of mass 40kg, within the range of ambient temperatures from-5 to 45°C. Data for the emu and 21 other species were used to calculate allometric relationships for resting ventilatory parameters in birds (breath frequency=13.5 mass^-0.314; tidal volume=20.7 mass^1.0). At low ambient temperatures the ventilatory system must accommodate the increased metabolic demand for oxygen. In the emu this was achieved by a combination of increased tidal volume and increased oxygen extraction. Data from emus sitting and standing at-5°C, when metabolism is 1.5x and 2.6x basal metabolic rate, respectively, indicate that at least in the emu an increase in oxygen extraction can be stimulated by low temperature independent of oxygen demand. At higher ambient temperatures ventilation was increased to facilitate respiratory water loss. The emu achieved this by increased respiratory frequency. At moderate heat loads (30–35°C) tidal volume fell. This is usually interpreted as a mechanism whereby respiratory water loss can be increased without increasing parabronchial ventilation. At 45°C tidal volume increased; however, past studies have shown that CO₂ washout is minimal under these conditions. The mechanism whereby this is possible is discussed.Abbreviations BMR basal metabolic rate - BTPS body temperature, ambient pressure, saturated - EO ₂ oxygen extraction - EWL evaporative water loss - f _R ventilation frequency - RH relative humidity - RHL respiratory heat loss - SEM standard error of the mean - SNK student-Newman-Keuls multiple range test - STPD standard temperature and pressure, dry - T _a ambient temperatures(s) - T _b body temperature(s) - T _ex expired air temperature(s) - T _rh chamber excurrent air temperature - V _J ventilation - VO₂ oxygen consumption - V _T tidal volume - V/Q air ventilation to blood perfusion ratio     

Regulation of ventilation in the caiman (Caiman latirostris): effects of inspired CO2 on pulmonary and upper airway chemoreceptors

In order to study the relative roles of receptors in the upper airways, lungs and systemic circulation in modulating the ventilatory response of caiman (Caiman latirostris) to inhaled CO₂, gas mixtures of varying concentrations of CO₂ were administered to animals breathing through an intact respiratory system, via a tracheal cannula by-passing the upper airways (before and after vagotomy), or via a cannula delivering gas to the upper airways alone. While increasing levels of hypercarbia led to a progressive increase in tidal volume in animals with intact respiratory systems (Series I), breathing frequency did not change until the CO₂ level reached 7%, at which time it decreased. Despite this, at the higher levels of hypercarbia, the net effect was a large and progressive increase in total ventilation. There were no associated changes in heart rate or arterial blood pressure. On return to air, there was an immediate change in breathing pattern; breathing frequency increased above air-breathing values, roughly to the same maximum level regardless of the level of CO₂ the animal had been previously breathing, and tidal volume returned rapidly toward resting (baseline) values. Total ventilation slowly returned to air breathing values. Administration of CO₂ via different routes indicated that inhaled CO₂ acted at both upper airway and pulmonary CO₂-sensitive receptors to modify breathing pattern without inhibiting breathing overall. Our data suggest that in caiman, high levels of inspired CO₂ promote slow, deep breathing. This will decrease dead-space ventilation and may reduce stratification in the saccular portions of the lung.     

Impact of Low Filter Resistances on Subjective and Physiological Responses to Filtering Facepiece Respirators

Ten subjects underwent treadmill exercise at 5.6 km/h over one hour while wearing each of three identical appearing, cup-shaped, prototype filtering facepiece respirators that differed only in their filter resistances (3 mm, 6 mm, and 9 mm H₂O pressure drop). There were no statistically significant differences between filtering facepiece respirators with respect to impact on physiological parameters (i.e., heart rate, respiratory rate, oxygen saturation, transcutaneous carbon dioxide levels, tympanic membrane temperature), pulmonary function variables (i.e., tidal volume, respiratory rate, volume of carbon dioxide production, oxygen consumption, or ventilation), and subjective ratings (i.e., exertion, thermal comfort, inspiratory effort, expiratory effort and overall breathing comfort). The nominal filter resistances of the prototype filtering facepiece respirators correspond to airflow resistances ranging from 2.1 - 6.6 mm H₂O/L/s which are less than, or minimally equivalent to, previously reported values for the normal threshold for detection of inspiratory breathing resistance (6 - 7.6 mm H₂O/L/sec). Therefore, filtering facepiece respirators with filter resistances at, or below, this level may not impact the wearer differently physiologically or subjectively from those with filter resistances only slightly above this threshold at low-moderate work rates over one hour.     

A system to simulate gas exchange in humans to control quality of metabolic measurements

We have developed a gas exchange simulation system (GESS) to assess the quality control in measurements of metabolic gas exchange. The GESS simulates human breathing from rest to maximal exercise. It approximates breath-by-breath waveforms, ventilatory output, gas concentrations, temperature and humidity during inspiration and expiration. A programmable motion control driving two syringes allows the ventilation to be set at any tidal volume (V _T), respiratory frequency (f), flow waveform and period of inspiration and expiration. The GESS was tested at various combinations of V _T (0.5–2.5 l) and f (10–60 stroke · min⁻¹) and at various fractional concentrations of expired oxygen (0.1294–0.1795); and carbon dioxide (0.0210–0.0690) for a pre-set flow waveform and for expired gases at the same temperature and humidity as room air. Expired gases were collected in a polyethylene bag for measurement of volume and gas concentrations. Accuracy was assessed by calculating the absolute and relative errors on parameters (error = measured−predicted). The overall error in the gas exchange values averaged less than 2% for oxygen uptake and carbon dioxide output, which is within the accuracy of the Douglas bag method. Accepted: 4 June 1998     

Cluster analysis of respiratory time series

We have investigated the respiratory control system with the hypothesis that, although many variables such as minute ventilation (V _I), tidal volume (V _T),breathing period (T _T),inspiratory duration (T _I),and exspiratory duration (T _E),may be observed, the controller functions more simply by manipulating only 2 or 3 of these. Thus, if tidal volume is the only independent variable, T _Ibeing determined by the off-switch threshold, these variables should have very similar time courses. Anesthetized dogs were subjected to CO₂ breathing and carotid sinus perfusion to stimulate both chemoreceptors. The time series of the variables V _I, V _T, T_T, T_Eand T _Ias well as P _{A CO 2}were determined on a breath by breath basis. Derived characteristics of these time series were compared using Cluster Analysis and the latent dimensionality of respiratory control determined by Factor Analysis. The characteristics of the time series clustered into 4 groups: magnitude (of the response), speed, variability and relative change. One respiratory factor accounted for 86% of the variance for the variability characteristics, 2 factors for magnitude (91%) and relative change (85%) and 3 factors for speed (89%). The respiratory variables were analysed for each of the 4 groups of characteristics with the following results: V _Tand T _I clustered together only for the magnitude and relative change characteristics where as T _Tand T _Eclustered closely for all four characteristics. One latent factor was associated with the [T _T-T_E]group and the other usually with P _{A CO 2}.Supported by USPHS 5t01 01919-05, NIH HL 12564 and GM 07033     

Control and evaluation of high-frequency jet ventilation: mechanical lung model

Ventilation systems that operate at high-frequency and deliver small volumes have the potential to provide adequate alveolar ventilation without excessive pulmonary pressures. One way of producing high-frequency ventilation is by use of jet bursts of an input gas through a cannula controlled by a solenoid valve. This high-frequency jet ventilation has yet to be quantitatively analysed for optimal clinical use. From an analysis of the jet-producing device, we obtained a quantitative relationship which allowed us to predict the gas volume of a jet burst (V_jet) from the driving pressure (P_d), and the jet duration (t_I). The device was applied to a mechanical lung model (a tube attached to an elastic bag corresponding to the lung airway and alveolar space). We examined how the control variables of the jet ventilation system changed the bag (alveolar) volume with respect to V_jet, the volume of entrained gas, and the volume of shunted gas. Using a nitrogen washout analysis, we evaluated the operating lung volume, effective dead-space volume (V_eds), and effective ventilation rate (V_eff). We found that V_eds is independent of the individual effects of jet cycle frequency, duty cycle, cannula diameter, and entrainment fraction. While V_eds was not affected significantly by the shape of the airway, it did depend on the distance of the jet cannula tip to the ventilated bag (or alveolar region) and on the tidal volume.     

Breathing during exercise in subjects with mild-to-moderate airflow obstruction: effects of physical training.

In this study we explored the effects of physical training on the response of the respiratory system to exercise. Eight subjects with irreversible mild-to-moderate airflow obstruction [forced expiratory volume in 1 s of 85 +/- 14 (SD) % of predicted and ratio of forced expiratory volume in 1 s to forced vital capacity of 68 +/- 5%] and six normal subjects with similar anthropometric characteristics underwent a 2-mo physical training period on a cycle ergometer three times a week for 31 min at an intensity of approximately 80% of maximum heart rate. At this work intensity, tidal expiratory flow exceeded maximal flow at control functional residual capacity [FRC; expiratory flow limitation (EFL)] in the obstructed but not in the normal subjects. An incremental maximum exercise test was performed on a cycle ergometer before and after training. Training improved exercise capacity in all subjects, as documented by a significant increase in maximum work rate in both groups (P < 0.001). In the obstructed subjects at the same level of ventilation at high workloads, FRC was greater after than before training, and this was associated with an increase in breathing frequency and a tendency to decrease tidal volume. In contrast, in the normal subjects at the same level of ventilation at high workloads, FRC was lower after than before training, so that tidal volume increased and breathing frequency decreased. These findings suggest that adaptation to breathing under EFL conditions does not occur during exercise in humans, in that obstructed subjects tend to increase FRC during exercise after experiencing EFL during a 2-mo strenuous physical training period.     

Spontaneous Breathing Pattern as Respiratory Functional Outcome in Children with Spinal Muscular Atrophy (SMA)

IntroductionSMA is characterised by progressive motor and respiratory muscle weakness. We aimed to verify if in SMA children 1)each form is characterized by specific ventilatory and thoraco-abdominal pattern(VTAp) during quiet breathing(QB); 2)VTAp is affected by salbutamol therapy, currently suggested as standard treatment, or by the natural history(NH) of SMA; 3)the severity of global motor impairment linearly correlates with VTAp.ResultsIn SMA1, a normal ventilation is obtained in supine position by rapid and shallow breathing with paradoxical ribcage motion. In SMA2, ventilation is within a normal range in seated position due to an increased respiratory rate(p<0.05) with reduced tidal volume(p<0.05) secondary to a poor contribution of pulmonary ribcage(%ΔV_RC,P, p<0.001). Salbutamol therapy had no effect on VTAp during QB(p>0.05) while tachypnea occurred in type I NH. A linear correlation(p<0.001) was found between motor function scales and VTAp.ConclusionA negative or reduced %ΔV_RC,P, indicative of ribcage muscle weakness, is a distinctive feature of SMA1 and SMA2 since infancy. Its quantitative assessment represents a non-invasive, non-volitional index that can be obtained in all children, even uncollaborative, and provides useful information on the action of ribcage muscles that are known to be affected by the disease.Low values of motor function scales indicate impairment of motor but also of respiratory function.     

Rates of breathing values and kinetics of respiration response in critical patterns of muscular activity in middle and long distance running

In elite runners, the ventilation influx, ventilation debt, and ventilation demand of the exercises were calculated on the basis of the pulmonary respiration dynamics during the maximum workout and recovery. The breathing values proved to closely reproduce the changes in the main parameters of oxygen demand at high intensity and duration of the exercise and can be used for quantification and standardization of exercise loads in sports. Three important factors of the aerobic exchange in the body were found to ensure the high level of the sports achievements in running: (1) general increase in the level of pulmonary ventilation (VE), oxygen demand (VO₂), and release of carbon dioxide (CO₂); (2) intensity of oxygen supply from lungs to the working muscles; (3) the rate of oxygenation (StO₂) and total rate of blood circulation.     

Monitoring Lung Aeration during Respiratory Support in Preterm Infants at Birth

Background

If infants fail to initiate spontaneous breathing, resuscitation guidelines recommend respiratory support with positive pressure ventilation (PPV). The purpose of PPV is to establish functional residual capacity and deliver an adequate tidal volume (V_T) to achieve gas exchange.

Objective

The aim of our pilot study was to measure changes in exhaled carbon dioxide (ECO₂), V_T, and rate of carbon dioxide elimination (VCO₂) to assess lung aeration in preterm infants requiring respiratory support immediately after birth.

Method

A prospective observational study was performed between March and July 2013. Infants born at <37 weeks gestational age who received continuous positive airway pressure (CPAP) or PPV immediately after birth had V_T delivery and ECO₂ continuously recorded using a sensor attached to the facemask.

Results

Fifty-one preterm infants (mean (SD) gestational age 29 (3) weeks and birth weight 1425 (592 g)) receiving respiratory support in the delivery room were included. Infants in the CPAP group (n = 31) had higher ECO₂ values during the first 10 min after birth compared to infants receiving PPV (n = 20) (ranging between 18–30 vs. 13–18 mmHg, p<0.05, respectively). At 10 min no significant difference in ECO₂ values was observed. V_T was lower in the CPAP group compared to the PPV group over the first 10 min ranging between 5.2–6.6 vs. and 7.2–11.3 mL/kg (p<0.05), respectively.

Conclusions

Immediately after birth, spontaneously breathing preterm infants supported via CPAP achieved better lung aeration compared to infants requiring PPV. PPV guided by V_T and ECO₂ potentially optimize lung aeration without excessive V_T administered.     

Slow Breathing and Hypoxic Challenge: Cardiorespiratory Consequences and Their Central Neural Substrates

Controlled slow breathing (at 6/min, a rate frequently adopted during yoga practice) can benefit cardiovascular function, including responses to hypoxia. We tested the neural substrates of cardiorespiratory control in humans during volitional controlled breathing and hypoxic challenge using functional magnetic resonance imaging (fMRI). Twenty healthy volunteers were scanned during paced (slow and normal rate) breathing and during spontaneous breathing of normoxic and hypoxic (13% inspired O₂) air. Cardiovascular and respiratory measures were acquired concurrently, including beat-to-beat blood pressure from a subset of participants (N = 7). Slow breathing was associated with increased tidal ventilatory volume. Induced hypoxia raised heart rate and suppressed heart rate variability. Within the brain, slow breathing activated dorsal pons, periaqueductal grey matter, cerebellum, hypothalamus, thalamus and lateral and anterior insular cortices. Blocks of hypoxia activated mid pons, bilateral amygdalae, anterior insular and occipitotemporal cortices. Interaction between slow breathing and hypoxia was expressed in ventral striatal and frontal polar activity. Across conditions, within brainstem, dorsal medullary and pontine activity correlated with tidal volume and inversely with heart rate. Activity in rostroventral medulla correlated with beat-to-beat blood pressure and heart rate variability. Widespread insula and striatal activity tracked decreases in heart rate, while subregions of insular cortex correlated with momentary increases in tidal volume. Our findings define slow breathing effects on central and cardiovascular responses to hypoxic challenge. They highlight the recruitment of discrete brainstem nuclei to cardiorespiratory control, and the engagement of corticostriatal circuitry in support of physiological responses that accompany breathing regulation during hypoxic challenge.     

Effect of anxiety on the function of the cardiorespiratory system

The effects of anxiety on the external respiration system and respiratory sinus arrhythmia (RSA) were studied in healthy subjects in real-life conditions. Changes in external respiration parameters and heart rate variability (HRV) in students going to take their end-of-term exams were assessed relative to a midterm period, and the cardiorespiratory system was monitored in a longitudinal study for 50 days. The function of the cardiorespiratory system was characterized by measuring external respiration parameters and calculating HRV parameters. State anxiety (SA) was assessed using Spielberger’s scale. An increase in SA before an exam was accompanied by a higher breathing rate, a higher tidal volume, and lower HRV indices, especially those related to respiratory sinus arrhythmia (HF and HF _norm). The changes in the parameters depended on the increase in SA. A negative correlation was observed between midterm HF and pre-exam SA. The longitudinal study revealed a distinct negative correlation between respiratory sinus arrhythmia parameters and peak expiratory flow (PEF) and a positive correlation between SA and PEF in the majority of subjects. Changes in cardiorespiratory parameters depended on the changes in SA in the longitudinal study. An increase in SA was accompanied by substantial changes in respiratory sinus arrhythmia (RAS) and external respiration parameters, and their correlation was assumed to indicate that modification of parasympathetic activity plays a leading role in increasing PEF.     

The ventilatory response to environmental hypercarbia in the South American rattlesnake,<Emphasis Type="Italic"> Crotalus durissus</Emphasis>

To study the effects of environmental hypercarbia on ventilation in snakes, particularly the anomalous hyperpnea that is seen when CO₂ is removed from inspired gas mixtures (post-hypercapnic hyperpnea), gas mixtures of varying concentrations of CO₂ were administered to South American rattlesnakes, Crotalus durissus, breathing through an intact respiratory system or via a tracheal cannula by-passing the upper airways. Exposure to environmental hypercarbia at increasing levels, up to 7% CO₂, produced a progressive decrease in breathing frequency and increase in tidal volume. The net result was that total ventilation increased modestly, up to 5% CO₂ and then declined slightly on 7% CO₂. On return to breathing air there was an immediate but transient increase in breathing frequency and a further increase in tidal volume that produced a marked overshoot in ventilation. The magnitude of this post-hypercapnic hyperpnea was proportional to the level of previously inspired CO₂. Administration of CO₂ to the lungs alone produced effects that were identical to administration to both lungs and upper airways and this effect was removed by vagotomy. Administration of CO₂ to the upper airways alone was without effect. Systemic injection of boluses of CO₂-rich blood produced an immediate increase in both breathing frequency and tidal volume. These data indicate that the post-hypercapnic hyperpnea resulted from the removal of inhibitory inputs from pulmonary receptors and suggest that while the ventilatory response to environmental hypercarbia in this species is a result of conflicting inputs from different receptor groups, this does not include input from upper airway receptors.Communicated by G. Heldmaier     

Influence of forward leaning and incentive spirometry on inspired volumes and inspiratory electromyographic activity during breathing exercises in healthy subjects

Breathing exercises (BE), incentive spirometry and positioning are considered treatment modalities to achieve lung re-expansion. This study evaluated the influence of incentive spirometry and forward leaning on inspired tidal volumes (V_T) and electromyographic activity of inspiratory muscles during BE. Four modalities of exercises were investigated: deep breathing, spirometry using both flow and volume-oriented devices, and volume-oriented spirometry after modified verbal instruction. Twelve healthy subjects aged 22.7 ± 2.1 years were studied. Surface electromyography activity of diaphragm, external intercostals, sternocleidomastoid and scalenes was recorded. Comparisons among the three types of exercises, without considering spirometry after modified instruction, showed that electromyographic activity and V_T were lower during volume-oriented spirometry (p = 0.000, p = 0.054, respectively). Forward leaning resulted in a lower V_T when compared to upright sitting (p = 0.000), but electromyographic activity was not different (p = 0.606). Inspired V_T and electromyographic activity were higher during volume-oriented spirometry performed after modified instruction when compared with the flow-oriented device (p = 0.027, p = 0.052, respectively). In conclusion BE using volume-oriented spirometry before modified instruction resulted in a lower work of breathing as a result of a lower V_T and was not a consequence of the device type used. Forward leaning might not be assumed by healthy subjects during situations of augmented respiratory demand.     

Respiratory evaporation in panting fowl: Partition between the respiratory and buccopharyngeal pumps

Summary Ventilation (V) and respiratory water loss were measured in domestic fowlGallus gallus subjected to raised environmental temperatures (33±2°C) and breathing air, 8% O₂ in N₂, 3% CO₂ in air or 5% CO₂ in air. Birds breathing air underwent an 18.6-fold increase in respiratory frequency and a 5-fold reduction in tidal volume and panting was accompanied by vigorous gular flutter. Hypoxic and hypercapnic birds breathed more slowly and deeply and gular flutter was strongly inhibited. The ratio was similar to that predicted on the basis of the measured ventilation assuming saturation of expired gas at measured gular mucosal temperature in hypoxic and hypercapnic birds but 54% greater than the predicted value in birds panting in air. It is concluded that the excess water loss during normal panting results from tidal airflow generated independently by the buccopharyngeal pump and that buccopharyngeal ventilation is equivalent to 54% of the respiratory ventilation.