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Biomedical subjects

P T Macklem

Publications and source records attributed to P T Macklem.

At least 163 records · Page 9Linked to original sources
PubMed1979

Influence of immersion to the neck in water on airway closure and distribution of perfusion in man.

We measured closing volume (CV), expiratory reserve volume (ERV) regional distribution of lung volume (Vr) and perfusion in 7 normal subjects in air and during immersion to the neck in water. In four subjects immersion resulted in a CV greater than ERV and the normal perfusion distribution became inverted. In the other subjects, ERV remained larger than CV and perfusion distribution during immersion was uniform, not inverted. In 5 subjects closing volume increased and in 3 of them, the ratio of apical/basal Vr increased significantly during immersion. One subject had nomeasurable CV and in the other it was not measured. The data suggest: (1) that when CV is greater than ERV during immersion there is an inversion of the normal perfusion distribution, caused by hypoxia and/or an increase in mean alveolar pressure in the alveoli beyond the closed airways, and (2) that an increase in pleural pressure gradient during immersion may contribute to the increase in C.V.

Adolescent↗
PubMed1979

Electromyogram pattern of diaphragmatic fatigue.

We studied the effect of breathing at various levels of transdiaphragmatic pressure (Pdi) on the EMG power spectrum of the diaphragm. The diaphragmatic EMG was measured simultaneously with a bipolar esophageal electrode (EE) and surface electrode (SE) placed on the ventral portion of the sixth and seventh intercostal spaces in five normal subjects breathing at functional residual capacity (FRC) against an inspiratory resistance. During each fatigue run the subjects generated a Pdi, with each inspiration, that was 25, 50, or 75% of maximum Pdi (Pdimax) for a period up to 15 min. During runs at 50 and 75% of the Pdimax, which are known to produce fatigue, we found for both EE and SE a progressive increase in the amplitude of the low-frequency (L = 20-46.7 Hz) and a decrease in the high-frequency (H = 150-350 Hz) component of the EMG. These changes were not seen at 25% of Pdimax. The diaphragmatic H/L ratio was independent of Pdi when the diaphragm was not fatigued. H/L fell while the diaphragm performed fatiguing work and this was more rapid at higher Pdi's. It was thus concluded that frequency spectrum analysis of the EMG can detect diaphragmatic fatigue reliably, prior to the time when the diaphragm fails as a pressure generator.

Diaphragm↗
PubMed1979

Demonstration of regional phase differences in ventilation by breath sounds.

We measured phase and amplitude of compensated breath sounds (Ib/Tn), which are indexes of regional ventilation, with two microphones placed near the apex and base 10 cm apart on the chest wall, lateral to the right anterior axillary line in four seated normal subjects. We compared phase and amplitude of Ib/Tn with phase and amplitude of esophageal pressure changes (Pes) measured by two balloons positioned 10 cm apart and at approximately the same horizontal levels as the microphones. When breathing tidally below closing volume (CV), apical Ib/Tn was louder and earlier than basal Ib/Tn, whereas basal Pes was greater and earlier than apical Pes. Above CV basal Ib/Tn was louder than apical and the phase differences either disappeared or followed phase differences in PES. The results suggest that below CV, ventilation of lower zones lags behind upper ones probably due to airway closure. Pes measurements indicate that this may lead to an amplification of pleural pressure swings at the base. Above CV, all airways are open, the ventilation of lower zones is greater than that of upper zones, and the sequence of ventilation follows the sequence of pleural pressure changes.

Adult↗
PubMed1979

Effect of pentobarbital anesthesia on rheology and transport of canine tracheal mucus.

Tracheal mucus samples were collected from six tracheostomized dogs before and after induction of pentobarbital anesthesia. The dynamic mechanical properties of the mucus were determined by the magnetic microrheometer technique. In 15 experiments, the mean value of elasticity at 1 rad/s rose from 67 dyn/cm2 before anesthesia to 212 dyn/cm2 in the period 15-90 min after induction. At the same time, mean viscosity at 1 rad/s rose from 24 to 79 P. The mucociliary transportability of some of the mucus samples was assayed by means of in vitro frog palate technique. In 10 experiments, the relative transport rate for dog tracheal mucus went from 98% of frog palate control befor anesthesia to 79% during pentobarbital anesthesia. A negative relationship between from palate transport rate and mucus elasticity was found. A negative correlation between transport and mucus viscosity at constant elasticity was also discovered. Finally, the mucus collection rate was reduced by a factor of about 8 during anesthesia, suggesting a reduction in the average depth of mucus.

Animals↗
PubMed1979

Fatigue of inspiratory muscles and their synergic behavior.

The time (tlim) required to produce inspiratory muscle fatigue was measured in five normal subjects breathing at functional residual capacity (FRC) against a variety of high inspiratory resistive loads. In every breathing test the subjects generated with each inspiration a mouth pressure (Pm) that was a predetermined fraction of maximum Pm (Pmmax). They continued breathing until they were unable to generate this Pm. The Pm/Pmmax that could be generated indefinitely (Pmcrit) was around 60%. The inspiratory power output at that level of breathing was 6.6 kg.m/min (Wcrit). In three of those subjects the same experiment was conducted at an end-expiratory volume of FRC + one-half inspiratory capacity (1/2IC). The higher lung volume was actively maintained by the subjects watching end-expiratory transpulmonary pressure on an oscilloscope. For any fraction of the maximum mouth pressure at FRC + 1/2IC (Pm'max), tlim was shorter than FRC. Pmcrit decreased to 30% Pm'max and Wcrit to 2.6 kg.m/min. Monitoring the abdominal pressure revealed that the contribution of the diaphragm and intercostal accessory muscles alternated in time, possibly postponing the onset of fatigue.

Diaphragm↗
PubMed1979

Pulmonary pressure-flow curves measured by a data-averaging circuit.

We measured pulmonary pressure-flow curves in nine normal nonsmoking subjects using a data-averaging circuit. With this method we obtained mean pressure flow curves of 20 consecutive breaths free of cardiac artifacts. Within-observer and within-subject-within-day reproducibility were good especially for the inspiratory limb of the curve. Within-subject-between-day variability in curvilinearity was substantial. In most subjects there was a continuous increase in resistance throughout the course of expiration even though the airways did not become dynamically compressed. This resulted in a mean value of expiratory resistance that was greater than during inspiration. Resistance early in expiration, however, was identical to that during inspiration. The data-averaging circuit allows for a more accurate assessment of the slope and the curvilinearity of pulmonary pressure-flow curves than other methods described before.

Airway Resistance↗
PubMed1979

A four-year follow-up study of lung mechanics in smokers.

We performed a prospective study of pulmonary function in 21 smokers, 9 ex-smokers, and 12 nonsmokers. The smokers and ex-smokers were preselected, because they were participants in a smoking cessation clinic. An average interval of 4 years separated the first and second (follow-up) studies. The smoking group showed a significant decrease in maximal expiratory flow measured at low lung volume, loss of elastic recoil, increase in lung compliance, increase in total lung capacity; increase in the ratio of residual volume to total lung capacity, and an increase in the ratio of functional residual capacity to total lung capacity. The ex-smokers showed changes similar to those of the smokers, but of lesser magnitude. The nonsmoking group demonstrated few changes in function during the study interval. Commonly measured parameters of function, including the ratio of the forced expiratory volume in 1 sec to the forced vital capacity and the maximal expiratory flow after exhalation of 50 per cent of the vital capacity, did not change significantly in any group. Sensitive tests of lung function were abnormal in a very high percentage of the combined group of smokers and ex-smokers when measured at the time of the second study; only a small number of abnormalities in these parameters were noted in the nonsmoking group. We conclude that there was a deterioration of lung function in smokers far in excess of that predicted by age. These changes suggest the development of emphysema and were predictable for the group as a whole by a high prevalence of abnormality of dynamic compliance, closing volume, maximal mid-expiratory flow, and residual volume at the time of the initial study.

Adult↗
PubMed1979

Relationship between the single-breath N test and age, sex, and smoking habit in three North American cities.

This report describes a collaborative study conducted in Montreal, Canada, Portland, Ore., and Winnipeg, Canada, to establish the relationship between the single-breath N2 test and age, sex, and smoking and to determine the prevalence of functional abnormalities in these populations. In nonsmokers, age-related regressions for closing volume, closing capacity, and the slope of phase III obtained from the single-breath N2 test, plus the ratio of the I-s forced expiratory volume to the forced vital capacity had very similar slopes, suggesting that differences in geographic location, climate, air pollution, and occupation had no effect on lung function detectable by these tests. Among the 6 city/six groups there was no systematic difference in the prevalence of functional abnormalities between the cities, but closing capacity expressed as a percentage of total lung capacity was abnormal most often in men and the slope of the alveolar plateau was abnormal most often in women. The prevalence of respiratory symptoms within different smoking categories was similar in the 3 cities. Although the number of cigarettes smoked had a significant effect on every test except the ratio of the I-s forced expiratory volume to forced vital capacity in men, the effect of age was considerably greater than the effect of smoking, and the dose-response relationship was weak. We conclude that additional factors may interact with smoking to place a smoker at risk of developing chronic airflow limitation.

Adult↗
PubMed1978

The relations between structural changes in small airways and pulmonary-function tests.

To examine the relation between small-airways abnormalities and specific lung functions, we performed pulmonary-function tests in 36 patients, of whom two were nonsmokers, one to three days before open-lung biopsy for localized pulmonary lesions. The primary lesion in the small airways was a progressive inflammatory reaction leading to fibrosis with connective-tissue deposition in the airway walls. Increase in disease in small airways correlated with deterioration in lung function. Lesions could be reliably detected (P less than 0.05) by tests for closing capacity, the volume at which air and helium flow ere equal (a test of airway caliber and elastic recoil), and the slope of phase III of the single-breath washout curve (which tests evenness of ventilation). These tests showed abnormalities at a time when the pathologic changes were still potentially reversible and when other tests were not appreciably changed.

Adult↗
PubMed1978

Partitioning of inspiratory pressure swings between diaphragm and intercostal/accessory muscles.

We tested the hypothesis that the inspiratory pressure swings across the rib-cage pathway are the sum of transdiaphragmatic pressure (Pdi) and the pressures developed by the intercostal/accessory muscles (Pic). If correct, Pic can only contribute to lowering pleural pressure (Ppl), to the extent that it lowers abdominal pressure (Pab). To test this we measured Pab and Ppl during during Mueller maneuvers in which deltaPab = 0. Because there was no outward displacement of the rib cage, Pic must have contributed to deltaPpl, as did Pdi. Under these conditions the total pressure developed by the inspiratory muscles across the rib-cage pathway was less than Pdi + Pic. Therefore, we rejected the hypothesis. A plot of Pab vs. Ppl during relaxation allows partitioning of the diaphragmatic and intercostal/accessory muscle contributions to inspiratory pressure swings. The analysis indicates that the diaphragm can act both as a fixator, preventing transmission of Ppl to the abdomen and as an agonist. When abdominal muscles remain relaxed it only assumes the latter role to the extent that Pab increases.

Diaphragm↗