Respiration physiology
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Respiration physiology · Dec 1991
Decreased pulmonary distensibility and pulmonary barotrauma in divers.
Pulmonary distensibility, lung volume and conductance were measured in 14 men (mean age 22 (SD 3) years) who suffered pulmonary barotrauma (PBT) during shallow water diving. Exponential analysis of static pressure-volume date obtained during deflation of the lungs gave K, and index of distensibility. The pulmonary conductance-recoil pressure (GL-PL) relationship was also obtained during deflation. ⋯ Decreased K reflects a decreased airspace size. Smaller airspaces increase the surface component of recoil pressure which increases the stress in tissue fibres. Relatively stiff airways may magnify the elastic stresses in peribronchial alveolar tissue increasing the possibility of rupture of alveolar walls with interstitial gas dissection.
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The increased alveolar-arterial oxygen gradient (A-aDO2) occurring at higher levels of exercise may reflect impaired gas mixing. This latter function was investigated using the multiple breath nitrogen washout technique in 30 physical training students (15 M, 15 F). They were examined at rest and at work loads of 50, 100 and 150 W, using a cycle ergometer. ⋯ Despite an increase in VDS from 156 +/- 33 to 258 +/- 35 ml and VDA from 139 +/- 40 to 305 +/- 73 ml, AME rose significantly with exercise from 72.5 +/- 5.0 to 78.3 +/- 3.3%. These results are discussed in relation to the morphology of the lung, and the stationary interface theory. They suggest that gas mixing improves at the onset of exercise only, so that the widening in A-aDO2 with increasing levels of exercise cannot be explained by impaired mixing efficiency alone, and is probably due to other factors such as critically rapid transit time of blood through the pulmonary capillaries as cardiac output increases.
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We evaluated whether the avian respiratory system displays the same fundamental mechanical behavior during external forcing as found in mammals. We measured airway flow and pressures in the trachea, air sacs and thoracoabdominal cavity in 4 anesthetized-paralyzed roosters during sinusoidal volume oscillations at the trachea in the normal range of euthermic breathing frequency, f(0.2 to 1.0 Hz), and tidal volume, VT (10-50 ml). From the pressure and flow waveforms, we calculated resistance (R) and elastance (E) of the total respiratory system and its major compartments (lungs, air sacs and chest wall). ⋯ Appl. Physiol. 69: 973-988. We conclude that, despite important anatomical differences between species, avian and mammalian respiratory tissues exhibit fundamentally similar mechanical behavior.
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In an attempt to understand the respiratory changes in abdominal muscle length in supine dogs (Ninane et al., 1988), we have recorded the electromyographic (EMG) activity of the transversus abdominis, external oblique, and rectus abdominis in eight supine, lightly anesthetized animals, and we have measured the respiratory changes in anteroposterior (AP) and transverse (T) diameters of the abdomen. Five animals had phasic expiratory EMG activity in the transversus during room air breathing, while only two animals had expiratory activity in the external oblique; no animal had phasic expiratory activity in the rectus. Activation of the transversus during expiration was invariably associated with a decrease in the abdominal T diameter and a rise in gastric pressure. ⋯ Conversely, these alterations in abdominal configuration increased in magnitude when expiratory activation of the transversus was increased by hyperoxic hypercapnia. These observations indicate that in supine dogs: (1) Expiratory contraction of the transversus acts primarily to reduce the transverse diameter of the abdomen; (2) This reduction, in turn, promotes an increase in abdominal pressure which results secondarily in an outward motion of the ventral abdominal wall; and (3) The latter may explain why the rectus abdominis, although electrically silent, shortens during expiration below its in situ relaxation length. The present observations also establish that in supine dogs breathing at rest, the abdomen does not move with a single degree of freedom.
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Respiration physiology · Feb 1989
Comparative StudyCardiac output effects of high-frequency oscillatory ventilation in normal dogs.
We compared the hemodynamic effects of high-frequency oscillatory ventilation (HFOV) with conventional continuous positive pressure ventilation (CPPV). Six mongrel dogs were anesthetized with chloralose and evaluated over a range of mean airway pressures (Pao) during CPPV and HFOV. Pao during HFOV was measured by allowing alveolar pressure to come into equilibrium with airway opening pressure and was set to equal mean Pao during CPPV. ⋯ Cardiac output as measured in triplicate by thermal dilution was similar between HFOV and CPPV at each level of mean airway pressure. After matching mean airway pressure and transmural Pwp we were unable to find any sparing effect of HFOV on cardiac output over a wide range of airway pressures. We conclude that there is not an independent effect of HFOV on cardiac output.