Journal of applied physiology: respiratory, environmental and exercise physiology最新文献

Pre- to postcapillary resistance ratios (Ra/Rv) and isogravimetric capillary pressures (Pc,i) were estimated using a modified filtration method and compared with estimates obtained by application of traditional isogravimetric techniques in isolated rat hindquarters and canine lungs. Pc,i's and Ra/Rv's were estimated using both methods in rat hindquarters perfused with whole blood or an artificial plasma and in blood-perfused canine lung. In each of the three experimental conditions studied, the modified filtration method yielded the same Pc,i and Ra/Rv as the isogravimetric technique. Maximal vasodilation of the rat hindquarter with papaverine reduced Ra/Rv approximately fourfold to a level which was not different from that obtained in hindquarters perfused with artificial plasma, although Pc,i was unchanged. These results indicate that the more easily applied modified filtration method provides an excellent measurement of Ra/Rv and Pc,i in whole organ studies.

The effects of adjacent large blood vessels, fibroelastic membrane, and parenchyma on pressure-diameter (P-D) behavior of intrapulmonary bronchi were studied in five dog lung lobes. Central lobar airways were inflated separately by blocking all branches with beads and inflating the distal lobar air spaces via pleural capsules. After bronchial P-D curves were obtained at fixed pleural pressures (Ppl) of -30, -10, and -5 cmH2O, the P-D properties of the isolated bronchi were measured in each of four stages of dissection: 1) lobar artery and vein were left attached to the bronchus, but parenchyma was removed to within 1-2 mm of the limiting membranes; 2) all remaining parenchyma was carefully removed; 3) the large vessels were removed, leaving the bronchial fibroelastic membrane intact; and 4) the fibroelastic membrane was peeled from the bronchus. From stage 1 it was deduced that in the intact lobes, peak peribronchial parenchymal stress (Px) averaged -29.2 cmH2O at Ppl = -30 cmH2O). In stage 2 bronchial recoil was reduced only approximately 5%. The major decrease (approximately 35%) occurred in stage 3, indicating that interaction between vessels and bronchi contributed significantly to bronchial stiffness. A final decrease of approximately 10% was seen in stage 4. We conclude that Px in the intact state is similar to Ppl at a transpulmonary pressure of 30 cmH2O and that stages 1 or 2 may provide a better basis for estimating Px than the commonly employed bronchus free of vessels and tissue.

This study 1) quantitates the effect of a 42.2-km footrace (marathon) on leg extensor strength (maximal peak torque, MPT) and work capacity (WC, measured during a leg extensor fatigue test), and 2) describes the effect of either a rest or exercise regimen for 1 wk after the marathon on the recovery of MPT and WC. Ten trained male runners performed personal records in a marathon and were then randomly assigned to either a rest or exercise-recovery group. The rest group did not train, whereas the exercise group ran 20-45 min/day at their selected intensity of exercise [50-60% maximal O2 consumption (Vo2max)] during the recovery week. MPT was measured at 1.1, 3.2, and 5.3 rad X s-1. The total work generated during a 50-contraction active extension-passive flexion fatigue test conducted at 3.2 rad X s-1 was defined as WC. Reports of perceived soreness of the quadriceps were obtained before each strength-testing session. These measurements were obtained before the marathon and 15-20 min and 1, 3, 5, and 7 days postmarathon. A significant reduction in MPT and WC resulted and continued 1 day postmarathon. MPT of both groups improved through day 5 postmarathon at 1.1 and 3.2 rad X s-1. MPT of the rest group improved through day 7 postmarathon but remained less than premarathon MPT. Recovery of MPT was impaired in the exercise group through days 5-7 postmarathon after 40-45 min exercise at 60% Vo2max. WC was recovered 3 days postmarathon in the rest group but was still impaired 7 days postmarathon in the exercise group.(ABSTRACT TRUNCATED AT 250 WORDS)

The upper airway is vulnerable to collapse from negative intraluminal pressures during inspiration. The tongue muscles, the genioglossi and geniohyoids, by contracting during inspiration, appear to function to resist this collapse. This study supports the hypothesis that two cervical strap muscles, the sternohyoid and sternothyroid, have a similar function. First, phasic inspiratory electromyographic activity was recorded from the sternohyoid and sternothyroid muscles of nine anesthetized rabbits during tidal breathing. Furthermore, each muscle showed a progressive increase in electromyographic activity with airway occlusion. Second, in eight rabbits, by determining the amount of negative pressure required to collapse the upper airway (airway closing pressure determination), it was shown that upper airway stability improved with electrical stimulation of either the paired sternohyoid or sternothyroid muscles. In addition, in 12 freshly killed rabbits, mechanical tension, mimicking the contraction of either the sternohyoid or sternothyroid, improved airway stability. Finally, observations of the pharyngeal lumen utilizing a fiber-optic endoscope, revealed concentric narrowing of the oro- and nasopharynx when airway pressure was lowered and concentric widening when tension was increased in the sternohyoid or sternothyroid muscles. These findings support the hypothesis that phasic inspiratory contraction of the sternohyoid and sternothyroid muscles functions to resist pharyngeal airway collapse due to negative intraluminal pressures.

Because of its potential relevance to heavy exercise we studied the ventilatory muscle function of five normal subjects before, during, and after shortterm near-maximal voluntary normocapnic hyperpnea. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made at four levels of ventilation: 76, 79, and 86% maximal voluntary ventilation (MVV) and at MVV. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made. The pressure-stimulation frequency relationship of the diaphragm obtained by unilateral transcutaneous phrenic nerve stimulation was studied in two subjects before and after hyperpnea. Decreases in maximal inspiratory (PImax) and transdiaphragmatic (Pdimax) strength were recorded posthyperpnea at 76 and 79% MVV. Decreases in the pressure-frequency curves of the diaphragm and the ratio of high-to-low frequency power of the diaphragm EMG occurred in association with decreases in Pdimax. Analysis of the pressure-time product (P X dt) for the inspiratory and expiratory muscles individually indicated the increasing contribution of expiratory muscle force to the attainment of higher levels of ventilation. Demonstrable ventilatory muscle fatigue may limit endurance at high levels of ventilation.

The position of small metallic markers embedded within the lung parenchyma and glued to the pleural surface of four excised right caudal dog lobes were determined during stepwise deflation from an airway opening pressure of 25 cmH2O in air-filled suspended lobes and 8 cmH2O in saline-filled lobes submerged in saline. Changes in the volumes of tetrahedrons formed by four noncoplanar markers were taken as regional lung volume changes at the centroids of the tetrahedron. In both air- and saline-filled lobes at all volumes below total lobe capacity (TLC) there was considerable variability in regional volume. The variability occurred at the first step below TLC and increased with deflation. Regions behaved consistently; regions that were proportionally larger or smaller than the overall lobe at any step tended to be larger or smaller, respectively, at all steps. There was a significant correlation between the regional behavior of the air- and saline-filled lobes. The variability of regional volume did not follow any clear topographical orientation. These results indicate there is considerable variability of lung compliance within small regions. This heterogeneity of regional parenchymal properties may be the anatomical basis of the nonuniformity of regional ventilation known to occur in intact animals and excised lobes within small regions at the same vertical height.

The maximum tetanic tension (Po) generated by a skeletal muscle is determined by its functional cross-sectional area (CSA) and its specific tension (tension/CSA). Measurements of average fiber length (normalized to a sarcomere length of 2.2 micron), muscle mass, and approximate angle of pinnation of muscle fibers within a muscle were taken from 26 different guinea pig hindlimb muscles and were used to calculate CSA. The specific tension was assumed to be 22.5 N X cm-2 and was used to determine the estimated Po of each muscle studied. In a second group of guinea pigs the in situ Po of 11 selected hindlimb muscles and muscle groups were determined. Estimated and measured Po values were found to have a strong linear relationship (r = 0.99) for muscle and muscle groups tested. The specific tension of the soleus, a homogeneously slow-twitch muscle, was shown to be approximately 15.4 N X cm-2 (P less than 0.01). Therefore, in our hands a specific tension value of 22.5 N X cm-2 appears to be a reasonable value for all mixed muscles studied in the guinea pig hindlimb and can be used to estimate their Po.

Thirty experiments were performed in two goats at an air temperature of +35 degrees C and a relative humidity of 33%. By means of heat exchangers, body core temperature (Tpaor) was adjusted to 39, 40.5, or 42 degrees C and maintained at these levels for 120 min. During the last 60 min the animals worked at a rate of 1.2 W/kg (treadmill, 3 km/h, 15%). Blood gases (arteriovenous O2 difference, Po2, Pco2), hemoglobin (Hb), blood lactate (LA), cardiac output (CO), blood pressure (MAP), heart rate (HR), metabolic rate (M), and respiratory evaporative heat loss (REHL) were determined. M, CO, HR, and Hb increased with exercise and were independent of Tpaor. At rest and exercise, REHL increased and Pco2 decreased at higher levels of Tpaor resulting in a respiratory alkalosis. During exercise this was accompanied by an increase in LA. At all instants, the concentrations of LA were higher at higher Tpaor. It is concluded that in a virtually nonsweating species like the goat the overall stress on the circulatory system caused by hyperthermia during exercise is relatively small while the behavior of blood LA is indicative of a temperature-dependent accumulation of LA also in the exercising muscle.

The hemodynamic and metabolic effects of exercise were measured in Crotalaria-induced pulmonary hypertension in rats. The Crotalaria group had increased preexercise heart rate, mean pulmonary arterial pressure (PAP), arteriovenous O2 content difference, right ventricular work index (RVWI), and total pulmonary vascular resistance index (TPVRI) and decreased mean systemic blood pressure (BP), arterial O2 content (CaO2), venous O2 content (CvO2), cardiac index (CI), stroke volume index (SVI), and left ventricular work index (LVWI). The Crotalaria group during exercise had increased PAP, RVWI, TPVRI, and total systemic vascular resistance index and decreased BP, O2 consumption, CaO2, CvO2, CI, SVI, LVWI, O2 pulse index, and exercise duration. It is hypothesized that abnormal right ventricular function was a primary factor in the reduced exercise tolerance of the Crotalaria group.