Breathing In Man Research Articles

Respiratory and circulatory responses to sustained positive‐pressure breathing and exercise in man

To investigate the effects of sustained positive-pressure breathing (PPB) on the adaptation of respiratory and circulatory functions to exercise, 8 healthy volunteers were exposed to PPB of air at 15 and 30 cm H2O in the supine position at rest and while performing leg exercise at 50% of individual maximal working capacity. PPB was both subjectively and objectively better tolerated when combined with exercise than it was at rest. PPB at 30 cm H2O resulted in marked hyperventilation with alkalosis in the resting condition, but did not significantly affect respiratory minute volume, blood gases or acid-base balance during exercise. Cardiac output and left ventricular work were reduced by about one fifth and one third, respectively, both at rest and during exercise. In contrast to the case at normal airway pressure, exercise-induced increase in cardiac output was accompanied by an increment in stroke volume during PPB. Although mean arterial pressure (relative to atmospheric) was elevated by PPB at rest and during exercise, the driving pressure in systemic circuits (arterial minus central venous pressure) was reduced in both conditions. It is concluded that dynamic exercise counteracts deleterious effects of PPB by normalizing respiratory function and by improving cardiac filling by activation of the leg muscle and the abdominal pumps.

Muscle activity during chest wall restriction and positive pressure breathing in man

The effects of sustained constriction of the rib cage (RCC), constriction of the abdomen (AC) and of breathing against a positive pressure of 10 cms of water (PPB) were studied in four normal subjects with moderate constant hypercapnia. Intercostal electrical activity (Eic) was measured by implanted wire electrodes and diaphragmatic electrical activity (Edia) by oesophageal electrodes. There was no fixed relation between Edia and V t. V t was unaltered during AC and RCC: Edia was unaltered during AC but increased during RCC. The response to PPB without constriction varied: three subjects increased end-expiratory V l with increase in Edia inspiratory Eic. One subject initially, and one subject after training, maintained end-expiratory V l constant with no change in Edia and an increase in expiratory Eic. When PPB was applied during AC and RCC there was an increase in Edia proportional to end-expiratory lung volume. The overall response to distortion was determined by voluntary choice, but muscle electrical activity reflected chest wall configuration: when the diaphragm was shorter and at a mechanical disadvantage its electrical activity increased. This was compatible with a reflex with afferent information from diaphragm tendon organ and muscle spindle receptors.

Volume, flow, and timing of each breath during positive-pressure breathing in man

This study is a breath-by-breath analysis of the effects of 5, 10, and 15 cmH2O positive-pressure breathing (PPB) on man's steady-state breathing pattern. Inspiratory (TI), expiratory (TE), and cycle (TT) durations, tidal volumes (VT), minute ventilation (VE), mean inspiratory flow rate (VT/TI), and mean expiratory flow rate (VT/TE) were determined from pneumotachograph and Wedge spirometer recordings before and during steady states on PPB. End-tidal CO2 was continuously recorded. Seventeen adults, seated in a full body-box, breathed quietly for 8 min through a mouthpiece on a bag-in-box. Pressure in the body-box was lowered to the desired level prior to 4 min of stress. On all pressure levels, end-expiratory volume, VT, VE, VT/TI, and VT/TE increased; end-tidal CO2, TE, and TT decreased with no consistent change in TI. Calculated alveolar ventilations indicated that the increases in VE were true hyperventilations. Each individual increased VE by using a unique combination of VT, TI, and TE. End-expiratory volume increased less and expiratory flow increased more than would occur passively. Hence, it is concluded that active reflexes account for the resistance of the systems to the passive distention, the facilitation of expiratory flow, and the shortening of TE.

Analysis of the effects of pulsatile capillary blood flow and volume on gas exchange

Blood flow into the pulmonary capillaries and the volume of blood within the capillary bed are both pulsatile with the cardiac cycle. We have developed a quantitative model of diffusional gas exchange in the lung to investigate the effects of coupling between these tow time-varying parameters on lung O 2 and CO 2 exchange. For normal man breathing room air at rest, the computed results agree well with previous predictions for the constant flow and volume case, and for the case of pulsatile flow alone. When coupled time-varying pulmonary capillary blood flow and volume are included, using the best data available in the literature to define these parameters, diffusional O 2 exchange is improved over the cases of pulsatile flow or volume alone, and closely approximates that obtained for hypothetical constant flow and volume case. CO 2 exchanges, O 2 exchange during hypoxia, are not affected by pulsatile flow and/or volume. These results suggest that O 2 exchange is efficient in the presence of coupled blood flow and blood volume pulsations as they exist in the lung capillaries. and that these conditions may be optima lfor gas exchange under certain physiological (or pathological) conditions.

Respiratory oscillations in discharge frequency of chemoreceptor afferents in sinus nerve and anaesthetized cats at normal and low arterial oxygen tensions.

1. The discharge of chemoreceptor afferents in preparations of the sinus nerve in spontaneously breathing anaesthetized cats has been subjected to an averaging procedure in records obtained when the animals breathed (a) air and (b) a hypoxic gas mixture. 2. The mean discharge frequency was higher in hypoxia than at normal oxygen tension. 3. Oscillations in chemoreceptor discharge frequency with the same period as respiration were obtained by the averaging procedure both at normal arterial oxygen tensions and in hypoxia, but there was no significant increase in oscillation amplitude with hypoxia. 4. The carotid body response to arterial PCO2 oscillations does not therefore appear to be amplified by hypoxia. This finding is discussed in relation to the reported dependence upon hypoxia of the ventilatory effects of tube breathing in man.

The pattern of stimulated breathing in man during non-elastic expiratory loading.

1. The pattern of breathing expressed as the relationship between tidal volume and the components of breath interval was studied in normal subjects during CO2 rebreathing, both under unloaded conditions and following the introduction of a non-elastic expiratory resistance. 2. Under unloaded conditions end-expiratory thoracic gas volume (FRC) measured plethysmographically did not alter during the course of the rebreathing experiment. Maximum tidal volume attained (VT, max.) was equal to or just less than the inspiratory capacity of the subject measured at rest. Expiratory reserve volume was not encroached upon even at the highest levels of ventilation. 3. Under loaded conditions the pattern of breathing was altered. VT, max. was diminished in all subjects and FRC showed a progressive rise during rebreathing which was proportional to the resistive load afforded by the artificial resistance. There were no consistent differences in the components of breath duration either at rest or on maximal ventilatory stimulation between the loaded and unloaded states. 4. It is suggested that the pattern of breathing adopted under conditions of expiratory non-elastic loading is influenced more by the secondary effects of breathing at an elevated lung volume, than by the effect of the non-elastic load per se.

Computer-aided measurement of breath volume and time components using magnetometers.

A computer-assisted method is developed for analyzing volume and time components of individual breaths using a previously developed magnetometer method for recording anteroposterior (AP) diameters of rib cage and abdomen. Calibration constants for the magnetometer system are computed during simultaneous measurements of airflow at the mouth for several breaths during spontaneous breathing. Tidal volume and inspiratory and expiratory times can then be computed from the magnetometer signals alone, without imposing respiratory devices at the subject's airway. No respiratory isovolume maneuvers are necessary. Results from normal subjects and from one patient with bilateral diaphragmatic paralysis show that the magnetometer analysis is closely comparable to standard measurements made from airflow recordings. The magnetometer technique thus provides an accurate means of measuring volume and time components of breathing in man, avoiding the behavioral or reflex effects induced by mouthpiece, nose clip, or face mask. Because no special respiratory maneuvers are required for calibration, the technique will be well suited to the study of breathing in those who are ill.

The effects of fentanyl and thiopental on breathing in man.

The effects of anesthetic agents on breathing in man are not well described. In part this reflects the difficulty in obtaining control measurements in awake man, without awareness of the subject that his breathing is being measured. In the present work we report a method for assessing respiratory volume changes in man by measuring body surface displacements. This method has the advantage that since measurements are not made at the mouth, subject awareness (and presumably behavioral alteration) of spontaneous breathing is minimized. An additional advantage of the present work is that continuous measurements of respiratory volume changes can be recorded prior to, during, and subsequent to the induction of general anesthesia. Because of the continuous nature of the measurement we hoped to be able to resolve the controversy concerning changes in functional residual capacity (FRC) and breathing pattern during anesthesia.KeywordsLung VolumeSpontaneous BreathingFunctional Residual CapacityBreathing PatternInspiratory CapacityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Assessment of the hypoxic drive to breathing in normal man and the effects and treatment of hypoxia in patients with chronic bronchitis and emphysema.

Assessment of the hypoxic drive to breathing in normal man and the effects and treatment of hypoxia in patients with chronic bronchitis and emphysema.

The relation between tidal volume and inspiratory and expiratory times during steady-state carbon dioxide inhalation in man.

1. Ambiguities and discrepancies in the published descriptions of the patterns of breathing in man have been re-investigated.Steady-state hyperpnoea during rest was induced in normal subjects of both sexes by means of CO(2) inhalation, usually in high O(2), but sometimes in low (P(A, O2) approximately 200 and 55 torr respectively).2. The relations between mean tidal volume V(T) and mean times for inspiration T(I) and expiration T(E) were satisfactorily divided into lower and upper parts (ranges 1 and 2) in nineteen out of thirty-three experiments using an objective least-squares method, and polynomials were fitted separately to each of the following pairs of variables V(T,lower), T(I); V(T,lower), T(E); V(T,upper), T(I); V(T,upper), T(E).3. The breakpoints occurred when V(T) was about one third of vital capacity, but there was much variation between subjects.4. In range 2, V(T) was inversely related to both T(I) and T(E) and there appeared to be linkage between T(I) and T(E), all as described by Clark & Euler (1972). The relation suggested by Hey, Lloyd, Cunningham, Jukes & Bolton (1966) over range 2 was not confirmed.5. The main part of the relation described by Hey et al. (1966) is concerned with range 1. Here the relation between V(T) and T(I) was variable; slight, but significant negative correlation predominated. V(T) was, on the other hand, strongly and inversely related to T(E), and plots of (T(E) - T(I)) against V(T) over both ranges showed even less scatter. Hence (a) T(E) is probably related to V(T) through two mechanisms, one involving a link with T(I) and another prominent one being quite independent of T(I), (b) most changes of respiratory frequency in normal man are brought about by change of T(E) rather than of T(I), and (c) there is no region of constant frequency as implied by Clark & Euler (1972).

A quantitative description of the pattern of breathing during steady-state CO2 inhalation in man, with special emphasis on expiration.

1. Quantitative data on the pattern of breathing in normal men and women (Gardner, 1977) have been used to derive expressions that are based on known physiological mechanisms.2. The relations between the applied chemical drive to breathing (expressed as DeltaP(A, CO2) in high O(2)) and the several components of the volume-time patterns described in the companion paper were examined. Neither mean tidal volume (V(T)), nor mean inspiratory nor mean expiratory times (T(I), T(E)) were uniquely related to the chemical drive across the breakpoint, which could be demonstrated in two and suspected in the third of these plots.3. Mean inspiratory flow (V(T)/T(I)) was linearly related to P(A, CO2) over the whole range and, like minute ventilation (V), showed no breakpoint. The mean relation was V(T)/T(I) = 0.11 (P(A, CO2) - 35.2). V(T)/T(I) was highly correlated with V; in individuals with healthy lungs and under relatively stable conditions of compliance and resistance it may be accepted as a wholly inspiratory alternative to V as an index, on the efferent side, of the total prevailing chemical drive.4. The description of the relation between T(I) and V(T) was essentially the same as that of Clark & Euler (1972): in range 1, T(I) = either 1.29 - 0.07 V(T)or the constant 1.24 sec, and in range 2, T(I) = 0.65/(V(T) - 0.88) + 0.59.5. Expiration was described by an equation based on the inverse linkage between T(E) and chemical drive and the direct link between both mean and breath-by-breath values of T(I) and T(E): T(E) = pT(I) + q/(drive - r) in which p was 0.64 +/- 0.09, q was 11.1 +/- 2.64 sec. (torr CO(2))(-1) and r was -2.73 +/- 1.09 torr CO(2). All three parameters were necessary for an adequate description.6. It is argued that the first term of the T(E) equation represents influences related to lung volume exerted through the vagus, and that the second represents the effects of over-all chemical stimulation exerted through other pathways.

A cybernetic model for the regulation of breathing in man

Summary In this paper, a comprehensive mathematical model of the human respiratory system is presented. This is capable of reproducing events occurring within the respiratory cycle and can be used as a test-bed for examining alternative hypotheses regarding the nature of the chemical control of breathing. The validity of these alternative controller structures is tested using feature space techniques of pattern recognition.

The relation between hypoxia and CO 2-induced reflex alternation of breathing in man

Four healthy young volunteers, selected for the responsiveness and steadiness of their breathing, were studied in rest and mild exercise while receiving alternate inspirates of low and high P CO 2 (0 and 8.6 kPa). P a CO 2 oscillated between ca. 6 and 7.5 kPa (45–55 torr). P O 2 was held steady at 4–7 levels between 6 and 28 kPa (45–210 torr). Thirteen separate inspiratory and expiratory variables (volumes, times, flows) were recorded and tested for reflex alternation. Matched controls were performed. Responses were generally small in relation to the scatter. Reflex alternation of any one variable was not always evident. The incidences of the responses were, in descending order, inspiratory flows and volumes, expiratory flows and volumes, expiratory duration; inspiratory duration alternated seldom, and then with only small amplitude. Reflex alternation was more likely to be observed in hypoxia than in euoxia or hyperoxia. A tendency for the incidences to be greater in exercise than at rest was not significant, but the amplitudes of alternation showed a significant difference in favour of exercise. In a substantial minority of experiments the amplitude of reflex alternation was significantly and positively correlated with hypoxia (1/(P a O 2 -C)). Alternation also occurred frequently in another substantial minority of experiments in which, however, there was no significant amplitude-hypoxia correlation. It was concluded that these two groups probably differed not so much in the form of the amplitude-hypoxia relation as in respect of the extent of the scatter in the observations. The results are consistent with interaction of non-steady-state with steady-state signals at the arterial chemoreceptors.

Impedance of the lungs-airways system during breathing in healthy man

Transpulmonary pressure ( P), mouth flow-rate ( V ̇ ), and volume ( V) were determined in twenty healthy subjects at two frequencies (0.5 and 2 Hz) and various flow-rate amplitudes. A Fourier analysis performed on P and V ̇ data allowed us to calculate the impedance function of the lungs-airways system in each individual. The latter function was shown to depend on the amplitude of flow-rate, indicating that the respiratory system is alinear primarily because of the alinearity of the respiratory resistance, R ∗ . A “true” impedance, Z, and phase, ϕ, were then calculated by extrapolating the describing function towards flow-rate of zero. The obtained Z and ϕ values are significantly different at 0.5 and 2 Hz: at 2 Hz Z is smaller and ϕ is approaching zero. These variations with frequency are the result mainly of a decrease of the respiratory elastance, E ∗ , probably due to gaseous inertia; the changes of R ∗ are small and are restricted to low flow-rates. They are possible related to changes of the glottis aperture during rapid breathing at low flow-rates. A comparison of the E ∗ and R ∗ values obtained from the Fourier analysis and E dyn and R dyn determined by means of the classical zero crossing techniques shows, in general, a satisfactory correspondence. However, R ∗ is systematically larger than R dyn: this is because R ∗ expresses the resistance over the total breathing cycle, whereas R dyn is the resistance value at low flow-rates. E dyn is slightly larger than E ∗ at 0.5 Hz and markedly smaller at 2 Hz. The difference at 0.5 Hz may be explained by the alinearity of the static P- V relationship of the lungs, whereas the discrepancy at 2 Hz may result from an underestimation of E dyn due to the presence of harmonics in P and V ̇ signals.

Effect of gas physical properties and flow on lower pulmonary resistance

We measured lower pulmonary resistance (Rlp) in eight dogs and three men breathing gas mixtures having different densities (p) and similar viscosities (mu). Rlp increased with gas density and with flow rate (V). In the dogs, these effects were not observed in lung segments subtended from 4-mm-ID bronchi; in more central airways, resistance varied approximately as (mup V)0.5. These results are compatible with Poiseuille flow in peripheral airways, and, in central airways, with flow resistance described by the equation of boundary layer growth. Rather than two discrete flow regimes, it is likely that flow patterns undergo a continual metamorphosis as Reynolds' numbers (Re) decrease between trachea and alveoli. Accordingly, the airways pressure-flow relationship is not described by any single fluid dynamics equation, but may be explained by the general equation, P = Kmu2-apa-1Va, where a reflects the proportion of inertial to viscous pressure losses and varies between 1 and 2 according to Re. Rohrer's equation described the observed pressure-flow relationships and predicted the change in Rlp with gas physical properties, suggesting a physical basis underlying this adequate mathematical description.

Relationships between eupnoeic pattern of breathing and ventilatory control in man II. Early response to transient hypercapnia.

The individual importance of peripheral chemosensitive afferents was studied using a transient hypercapnia (inhalation of a 5% or a 10% CO2 in air gas mixture respectively during 4 or 2 breaths) in human conscious subjects chosen for their different eupnoeic ventilatory patterns. Calculation of the speed of change in end-tidal CO2 pressure in tracheal gas (sPETCO2) and of the rate of change in tidal volume (sVI) gave assessment for quantifying the sensitivity of arterial chemoreceptors to hypercapnia (sCO2=SVI/SPETCO2). Our results showed that, independently of any outside influence of the eupnoeic ventilatory pattern on the components of the chemical stimulus, sVI and sCO2 were found to be much smaller in subjects whose pattern of breathing was slow (i.e. having a large tidal volume). The possible causes of the weak importance of peripheral chemosensitive afferents in such subjects were discussed.

Methods of studying the control of breathing in experimental animals and man

Methods of studying the control of breathing in experimental animals and man

Relationships between eupnoeic pattern of breathing and ventilatory control in man: I. Response to airways occlusion during active lung inflation.

The apnoeic response following interruption of the air flow at different levels of the inspiratory capacity (deltaVL) was studied in conscious children and adults. Changes in mouth pressure were used to measured the duration of the apnoe. The total duration of the interrupted breath (T1) was compared to mean value of the ventilatory period of the five preceding breaths (T0). A monoexponential regression could be fitted to the relationship between T1/T0 ratio and change in lung volume (deltaVL) measured at the onset of interruption: T1/T0=k-exp (S-deltaVL), S begin the sensitivity of the response to lung inflation. When T1/T0=1, the intrathoracic lung volume was called threshold volume (VTh.L.). The parameters S and VTh.L. were used for characterization of the individual importance of the Breuer-Hering inspiratory-inhibitory reflex (B.H. reflex). The high reproducibility of the T1/T0 vs. deltaVL relationship in many subjects showed the light influence of voluntary control on apnoea's duration. In each subject, S and VTh.L. were compared with ventilatory variables measured during eupnoea. A fast pattern of breathing (i.e. small inspired volume and short inspiratory duration) was associated with high value of S and low VTh.L. Moreover VTh.L. was near the tidal volume range in subjects where the B.H. reflex was the more potent. Thus, vagal afferents relating to this reflex could modulate the eupnoeic pattern of some subjects.

Influence of hypoxia and hyperoxia on subcutaneous adipose tissue blood flow in man.

Subcutaneous adipose tissue blood flow (ATBF) was measured by the 133Xe washout method in normal men breathing oxygen at partial pressures from 0.1 to 2 atmospheres. Breathing oxygen at partial pressures of 0.1 and 1 atm. increased and reduced ATBF by 56% and 26%, respectively as compared to air breathing. These effects were highly significant. Breathing of oxygen at 2 atm. partial pressure had no consistent effect on ATBF, although considerable changes--positive or negative--could been seen in some experiments. Oxygen-breathing at 1 atm. partial pressure is associated with a slight hyperventilation and fall in PACO2. This was shown to be without importance for the effect of oxygen on adipose tissue blood flow.

Muscular respiratory receptors in self-regulation of normal breathing in man.

In man, in the process of evolution the proprioceptive reflexes from the chest muscle during apnea become weak. Probably the impulses from the respiratory stretch receptors do not take part in self-regulation of eupnea.