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Biomedical subjects

D F Rochester

Publications and source records attributed to D F Rochester.

At least 37 records · Page 2Linked to original sources
PubMed1989

Prolonged relaxation rate of inspiratory muscles in patients with sleep apnea.

To evaluate whether inspiratory muscle function is impaired in patients with sleep apnea, we measured inspiratory muscle strength and relaxation rate before and after sleep in 13 patients. The sleep apnea group was composed of eight patients with severe obstructive sleep apnea, and the non-apnea group was composed of five patients without significant sleep apnea. We chose the time constant of relaxation (TauR) as an index of impaired inspiratory muscle contractility, and in subsets of each group, we measured the inspiratory pressure-time index as an indicator of a fatiguing breathing pattern. In patients with sleep apnea, presleep TauR was 79 +/- 22 ms (SD), longer than that of normal subjects (normal, 59 +/- 7 ms) (p less than 0.05). TauR increased by 21 +/- 16 ms during sleep (p less than 0.01). In patients without apnea, presleep TauR was 67 +/- 7 ms and it did not change after sleep. Maximal inspiratory and expiratory pressures were unchanged after sleep. We conclude that patients with sleep apnea do not develop overt inspiratory muscle failure but do have impaired contractility. We speculate that hypoxemia as well as increased work load was responsible.

Adult↗
PubMed1988

Effects of a chronic wasting infection on skeletal muscle size and contractile properties.

To evaluate the effects of chronic infection on skeletal muscle dimensions and contractile properties, we used a hamster model of visceral leishmaniasis, a parasitic infection of the reticuloendothelial system produced by Leishmania donovani (LD). To distinguish between effects of reduced caloric intake and infection per se, we also studied healthy control animals and noninfected animals subjected to caloric restriction. Three muscles were tested in vitro: plantaris, soleus, and diaphragm. Both caloric restriction and LD infection caused loss of body weight and reduced muscle cross-sectional areas and wet weights. The interventions had variable effects on in vitro contractile properties, the most pronounced being reduction in peak tension in response to tetanic stimulation. Tension loss was 35-45%, except for a loss of 65% in plantaris of LD-infected animals. We conclude that chronic LD infection affects skeletal muscles in both indirect and direct ways. 1) Reduced caloric intake due to anorexia decreases muscle size and active tension. Disuse probably enhances this effect in limb muscles. 2) Infection produces profound weakness of inactive fast-twitch muscle by unknown mechanisms.

Animals↗
PubMed1988

Vagal afferents, diaphragm fatigue, and inspiratory resistance in anesthetized dogs.

This study tests three hypotheses regarding mechanisms that produce rapid shallow breathing during a severe inspiratory resistive load (IRL): 1) an intact vagal afferent pathway is necessary; 2) diaphragm fatigue contributes to tachypnea; and 3) hypoxia may alter the pattern of respiration. We imposed a severe IRL on pentobarbital sodium-anesthetized dogs, followed by bilateral vagotomy, then by supplemental O2. IRL alone produced rapid shallow breathing associated with hypercapnia and hypoxia. After the vagotomy, the breathing pattern became slow and deep, restoring arterial PCO2 but not arterial PO2 toward the control values. Relief of hypoxia had no effect, and at no time was there any evidence of fatigue of the diaphragm as measured by the response to phrenic nerve stimulation. We conclude that an intact afferent vagal pathway is necessary for the tachypnea resulting from a severe IRL, neither hypoxia nor diaphragm fatigue played a role, and, although we cannot rule out stimulation of vagal afferents, the simplest explanation for the increased frequency in our experiments is increased respiratory drive due to hypercapnia.

Afferent Pathways↗
PubMed1988

Short-term entrainment of ventilation to the walking cycle in humans.

We describe a breath-by-breath method to test for entrainment of breathing and walking cycles. Thirty-eight normal subjects walked comfortably on a treadmill while breathing through a pneumotachograph. We analyzed the time intervals between heel strikes and the onset of inspiration (or expiration) for evidence of phase locking between steps and breaths, using Monte Carlo simulation to model the probability that n consecutive inspirations (or expirations) would begin at a constant time interval +/- 0.10 s from heel strikes by chance. We developed empirical criteria for rhythm synchronization during series of four or more breaths, while maintaining an estimated specificity of 95%. The majority of subjects showed some evidence of entrainment (29 +/- 23% of breaths on average), which occurred intermittently, usually lasting less than 10 breaths at a time. The precision of phase locking during spontaneous entrainment was similar to that in 10 subjects who attempted to maintain deliberate entrainment. The results suggest that the walking cadence provides a persuasive, but not dominant, input to the central breathing pattern generator. The present method can detect entrainment even when it occurs sporadically or with varying coupling pattern.

Adult↗
PubMed1988

Functional characteristics of canine costal and crural diaphragm.

We estimated the in situ force-generating capacity of the costal and crural portions of the canine diaphragm by relating in vitro contractile properties and diaphragmatic dimensions to in situ lengths. Piezoelectric crystals were implanted on right costal and left crural diaphragms of anesthetized dogs, via midline laparatomy. With the abdomen reclosed, diaphragm lengths were recorded at five lung volumes. Contractile properties of excised muscle bundles were then measured. In vitro force-frequency and length-tension characteristics of the costal and crural diaphragms were virtually identical; their optimal force values were 2.15 and 2.22 kg/cm2, respectively. In situ, at residual volume, functional residual capacity (FRC), and total lung capacity the costal diaphragm lay at 102, 95, and 60% of optimal length (Lo), whereas the crural diaphragm lay at 88, 84, and 66% of Lo. Muscle cross-sectional area was 40% greater in costal than in crural diaphragms. Considering in situ lengths, cross-sectional areas, and in vitro length-tension characteristics at FRC, the costal diaphragm could exert 60% more force than the crural diaphragm.

Animals↗
PubMed1988

Characteristics and functional significance of canine abdominal muscles.

To assess the characteristics and function of the muscles of the anterolateral abdominal wall, we have examined the isometric contractile properties of bundles of canine rectus abdominis (RA) and external oblique (EO) muscles. In addition, we have related the lengths of these muscles measured sonometrically in vivo at supine functional residual capacity (FRC) to in vitro optimal force-producing length (Lo). We also investigated the action of the abdominal muscles on the displacement of costal and crural diaphragm. We found that 1) contraction time of RA was longer and that the RA developed greater force than the EO at submaximal stimulation frequencies; 2) maximal tetanic force and the active length-tension curves were similar in both abdominal muscles; 3) on passive stretch, the compliance of the RA was one-third that of the EO; 4) at supine FRC, the EO is operating at 83% of Lo, whereas the RA is operating at 105% of Lo; 5) stimulation of either RA or EO (abdominal pressure of 15 cmH2O) lengthened the costal and crural diaphragm toward their Lo values, with greater crural excursion occurring than costal. We conclude that the RA is well suited for restraining the abdominal viscera in prone quadrupeds, whereas the EO is better designed to assist expiration. Stimulation of both muscles improves in situ diaphragmatic operating length.

Abdominal Muscles↗
PubMed1988

Electrical and mechanical activity in the human lower esophageal sphincter during diaphragmatic contraction.

To determine the effect of contraction of the diaphragm on the lower esophageal sphincter (LES) pressure, we studied eight healthy volunteers during spontaneous breathing, maximal inspiration, and graded inspiratory efforts against a closed airway (Muller's maneuver). Electrical activity of the crural diaphragm (DEMG) was recorded from bipolar esophageal electrodes, transdiaphragmatic pressure (Pdi) was calculated as the difference between gastric and esophageal pressures, and LES pressure was recorded using a sleeve device. During spontaneous breathing, phasic inspiratory DEMG was accompanied by phasic increases in Pdi and LES pressure. With maximal inspiration, DEMG increased 15-20-fold compared with spontaneous inspiration, and LES pressure rose from an end-expiratory pressure of 21 to 90 mmHg. Similar values were obtained during maximal Muller's maneuvers. LES pressure fell promptly when the diaphragm relaxed. Graded Muller's maneuver resulted in proportional increases in the Pdi, LES pressure, and DEMG. The LES pressure was always greater than Pdi and correlated with it in a linear fashion (P less than 0.001). We conclude that the contraction of the diaphragm exerts a sphincteric action at the LES, and that this effect is an important component of the antireflux barrier.

Atmospheric Pressure↗
PubMed1988

Tests of respiratory muscle function.

Respiratory muscle strength and endurance should be assessed when dyspnea, respiratory failure, or poor performance on routine pulmonary function tests are unexplained. Respiratory muscle strength can be measured non-invasively from maximal mouth pressures, but measurement of transdiaphragmatic pressure refines the assessment. The maximal voluntary ventilation test is the only simple index of ventilatory or respiratory muscle endurance. Other tests for endurance and fatigue are more difficult, but some newer techniques may be applicable to the clinical laboratory. Some patients who exhibit tachypnea, marked use of neck inspiratory muscles, and chest-abdomen asynchrony may be developing respiratory muscle fatigue.

Electromyography↗
PubMed1987

Effect of the diaphragmatic contraction on lower oesophageal sphincter pressure in man.

The effect of diaphragmatic contraction and relaxation on the lower oesophageal sphincter (LOS) pressure was studied in 10 healthy volunteers. Pressures in the oesophagus, LOS, and stomach were measured in three phases. Phase I, end tidal expiration; phase II, subjects inspired to total lung capacity (TLC) and kept the airway open (sustained diaphragmatic contraction); and phase III, at TLC subjects relaxed against a closed glottis (diaphragm relaxed). The LOS pressure in phase II was significantly higher than in phase I, while in phase III it was significantly lower compared with phase I. There was a net increase in LOS pressure of 32 mmHg in phase II as compared to phase I. After phase II, as subjects moved into phase III, there was a sudden drop in the LOS pressure. The LOS pressure in phase II correlated with the transdiaphragmatic pressure in a linear fashion. These observations suggest that diaphragmatic contraction in man enhances the LOS pressure and this augmentation of sphincter tone may be a vital component of the antireflux mechanism.

Adult↗
PubMed1987

COPD and human diaphragm muscle dimensions.

To assess the effect of COPD on diaphragm muscle dimensions, we measured diaphragm muscle mass, thickness, area, and lengths in 18 COPD patients at necropsy. We compared these results with data obtained from 22 non-COPD patients matched with regard to age, height, weight, and sex distribution. In the COPD patients, diaphragm muscle mass was 213 +/- SD 69 g, thickness was .320 +/- .055 cm, area was 647 +/- 160 cm2, coronal muscle length was 27.8 +/- 4.0 cm and sagittal muscle length was 15.8 +/- 2.8 cm. These values were within +/- 8 percent of the comparable values in the non-COPD patients, with no significant differences. There was no correlation between diaphragm length and lung volume in 13 COPD patients with TLC and ten with RV measurements. We conclude that over the range of lung volume encountered (TLC 135 +/- 28 percent predicted, RV 102 +/- 29 percent predicted TLC), there is no evidence for permanent shortening of the diaphragm.

Adaptation, Physiological↗
PubMed1986

Contractile characteristics and operating lengths of canine neck inspiratory muscles.

The neck inspiratory muscles are recruited to support breathing under numerous conditions. To gain insight into their synergistic actions we examined the isometric contractile properties of bundles from canine scalene and sternomastoid muscles. In addition, we also related the length of the neck muscles, measured sonomicrometrically in vivo at different lung volumes and body positions, to their optimal force-producing length (Lo) determined in vitro. We found that the speed of the sternomastoid is somewhat faster than that of the scalene owing to a shorter relaxation rate; the sternomastoid generates higher forces at submaximal stimulation frequencies than the scalene; the maximal tetanic force corrected for cross-sectional area is the same for both neck muscles; the neck muscles are significantly faster than the canine costal diaphragm; at supine functional residual capacity (FRC), the scalene is operating at a length corresponding to 85% Lo, whereas the sternomastoid is significantly shorter at 75% Lo; increasing lung volume shortens both muscles slightly, the length at supine total lung capacity being approximately 5% shorter than at FRC; and in the upright posture, both neck muscles lengthen toward their Lo, with the sternomastoid lengthening more than the scalene. We conclude that the scalene is a more effective force generator than the sternomastoid with the animal lying supine; the neck muscles appear to maintain their force-generating potential regardless of the lung volume; and the force-generating potential of the neck muscles is greatly enhanced with the animal in the upright vs. the supine position. This may contribute to the augmented rib cage motion characteristic of breathing in the upright posture.

Animals↗
PubMed1986

Malnutrition and the respiratory muscles.

Malnutrition reduces respiratory muscle mass and contractile force through atrophy of Type II fibers and impaired energy metabolism. Nutritional repletion restores respiratory muscle function, but may add to ventilatory work. Nutritional repletion also enhances weaning from mechanical ventilation.

Animals↗
PubMed1985

Steady-state response of conscious man to small expiratory resistive loads.

To determine the predominant steady-state ventilatory responses to mild expiratory flow-resistive loads, we subjected 14 normal subjects to expiratory resistances of 0-10 cm H2O/L/sec (R0-R3). Breathing patterns and abdominal muscle activity (EMG) were recorded during quiet breathing, and when ventilation was augmented by dead space breathing (7 subjects) or treadmill walking (7 subjects). Expiratory loading increased expiratory time (TE), tidal volume and mean inspiratory flow rate, while decreasing inspiratory duty cycle and respiratory frequency. Minute ventilation (VI) remained constant. These load responses were most prominent during quiet breathing, and were attenuated or abolished as VI increased. Abdominal EMG was negligible during quiet breathing, increased when VI increased, but showed no consistent response to R1-R3. Thus, the principal defense against mild expiratory loads is prolongation of expiration, accompanied by enhanced inspiratory drive. Abdominal muscle expiratory activity is elicited by increasing ventilation, but occurs only sporadically with expiratory loading of the magnitude studied.

Abdominal Muscles↗