Biomedical subjects

F D McCool

Publications and source records attributed to F D McCool.

At least 37 records · Page 2Linked to original sources

PubMed1994

Pressure-flow specificity of inspiratory muscle training.

The inspiratory muscles (IM) can be trained by having a subject breathe through inspiratory resistive loads or by use of unloaded hyperpnea. These disparate training protocols are characterized by high inspiratory pressure (force) or high inspiratory flow (velocity), respectively. We tested the hypothesis that the posttraining improvements in IM pressure or flow performance are specific to training protocols in a way that is similar to force-velocity specificity of skeletal muscle training. IM training was accomplished in 15 normal subjects by use of three protocols: high inspiratory pressure-no flow (group A, n = 5), low inspiratory pressure-high flow (group B, n = 5), and intermediate inspiratory pressure and flow (group C, n = 5). A control group (n = 4) did no training. Before and after training, we measured esophageal pressure (Pes) and inspiratory flow (VI) during single maximal inspiratory efforts against a range of external resistances including an occluded airway. Efforts originated below relaxation volume (Vrel), and peak Pes and VI were measured at Vrel. Isovolume maximal Pes-VI plots were constructed to assess maximal inspiratory pressure-flow performance. Group A (pressure training) performed 30 maximal static inspiratory maneuvers at Vrel daily, group B (flow training) performed 30 sets of three maximal inspiratory maneuvers with no added external resistance daily, and group C (intermediate training) performed 30 maximal inspiratory efforts on a midrange external resistance (7 mm ID) daily. Subjects trained 5 days/wk for 6 wk. Data analysis included comparison of posttraining Pes-VI slopes among training groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Measurements of ventilation in freely ranging subjects.

Both the level of ventilation and breathing pattern (breathing frequency, inspiratory time, and tidal volume) have an important influence on particle deposition and gas uptake in the lungs. Accordingly, a description of these measures is needed to assess better the dose of particulate deposit and gas uptake in the lungs during varied activities. The long-term objectives of this study were to develop a means of measuring minute ventilation in the field by using body surface displacements, and to evaluate the utility of heart rate as an index of minute ventilation. By using respiratory inductance plethysmographic belts and magnetometers placed on the rib cage and abdomen, ventilation and breathing pattern can be noninvasively measured in mobile individuals. Our specific aims were (1) to validate measurements of ventilation using body surface displacement; (2) to describe breathing patterns in subjects performing a variety of daily activities in the laboratory; (3) to analyze relationships between minute ventilation and heart rate; and (4) to measure ventilation in the field with one technique utilizing body surface displacements and another based upon heart rate. We found that values of tidal volume, inspiratory time, and breathing frequency derived from body surface displacement measurements correlated well with those determined spirometrically during a variety of activities. The coefficient of determination for tidal volume was 0.97 +/- 0.2 for cycling, 0.93 +/- 0.07 for arm cranking, 0.91 +/- 0.05 for pulling, and 0.84 +/- 0.12 for lifting. Our experiments showed that the breathing pattern was altered by the use of a mouthpiece and varied according to the type of activity. The use of a mouthpiece increased tidal volume by 34%, decreased the breathing frequency by 10%, and increased minute ventilation by 16%. There was more variability of these parameters during lifting and pulling activities than during cycling. The ventilation-heart rate relationship varied from subject to subject and was altered by the use of a mouthpiece. We found that ventilation measured in the field from body surface displacement correlated well with ventilation measured using the pneumotachograph (R2 = 0.89). However, measurements of ventilation derived from heart rate were not as accurate as those derived from body surface displacements. We concluded that minute ventilation can be measured accurately using body surface displacements in the laboratory and in the field. Heart rate can also be utilized, but factors affecting the minute ventilation-heart rate relationship, such as the use of a mouthpiece and range of heart rate, must be addressed to obtain more accurate estimates of minute ventilation.

Adolescent↗

PubMed1992

Effect of fatigue on maximal inspiratory pressure-flow capacity.

The inspiratory muscles can be fatigued by repetitive contractions characterized by high force (inspiratory resistive loads) or high velocities of shortening (hyperpnea). The effects of fatigue induced by inspiratory resistive loaded breathing (pressure tasks) or by eucapnic hyperpnea (flow tasks) on maximal inspiratory pressure-flow capacity and rib cage and diaphragm strength were examined in five healthy adult subjects. Tasks consisted of sustaining an assigned breathing frequency, duty cycle, and either a "pressure-time product" of esophageal pressure (for the pressure tasks) or peak inspiratory flow rate (for the flow tasks). Esophageal pressure was measured during maximal inspiratory efforts against a closed glottis (Pesmax), maximal transdiaphragmatic pressure was measured during open-glottis expulsive maneuvers (Pdimax), and maximal inspiratory flow (VImax) was measured during maximal inspiratory efforts with no added external resistance before and after fatiguing pressure and flow tasks. The reduction in Pesmax) with pressure fatigue (-25 +/- 7%) was significantly greater than the change in Pesmax with flow fatigue (-8 +/- 8%, P less than 0.01). In contrast, the reductions in Pdimax (-11 +/- 8%) and VImax (-16 +/- 3%) with flow fatigue were greater than the changes in Pdimax (-0.6 +/- 4%, P less than 0.05) or VImax (-3 +/- 4%, P less than 0.05) with pressure fatigue. We conclude that respiratory muscle performance is dependent not only on the presence of fatigue but whether fatigue was induced by pressure tasks or flow tasks. The specific impairment of Pesmax and not of Pdimax or flow with pressure fatigue may reflect selective fatigue of the rib cage muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗

PubMed1992

Oxygen cost of resistive-loaded breathing in quadriplegia.

We hypothesized that, in quadriplegia, chest wall distortion would increase the energy cost of ventilation. To assess this, we measured the oxygen cost of breathing (VO2 resp) and changes in chest wall configuration during inspiratory resistive-loaded breathing tasks in five quadriplegic and five normal subjects. Each subject performed three breathing tasks that spanned a range of work rates (Wtot). Configurational changes of the abdomen and upper, lower, and transverse rib cage were assessed with magnetometers. We found that 1) in both groups, VO2resp increased linearly with Wtot over the range of tasks performed, 2) the mean slope of the regression line of VO2resp vs. Wtot was greater for quadriplegic than for normal subjects (3.7 +/- 0.8 vs. 2.0 +/- 0.7 ml O2/J, P less than 0.01), 3) efficiency of breathing (Wtot/VO2resp) was less for quadriplegic than for normal subjects (1.9 +/- 0.6 vs. 3.5 +/- 1.4%, P less than 0.001), 4) during inhalation, upper and lower rib cages behaved similarly in the two groups, but the quadriplegic subjects had a decrease in transverse rib cage and a much greater increase in abdomen than normal subjects, and 5) functional residual capacity decreased in normal but not in quadriplegic subjects during the breathing tasks. We conclude that the lesser efficiency of breathing in quadriplegia may be related to the elastic work of chest wall distortion, shorter mean operational diaphragm length, and possibly differences between normal and quadriplegic subjects in mechanical advantage of available inspiratory muscles.

Adult↗

PubMed1992

Breathing patterns during varied activities.

The level of ventilation attained and breathing patterns adopted during activity have important implications for the distribution and deposition of particles that are inhaled. However, breathing patterns and levels of ventilation adopted during specific physical activities are unknown. We used a noninvasive means of measuring ventilation in subjects performing a variety of activities (bicycling, arm ergometry, lifting, and pulling) during unencumbered (no mouthpiece) breathing and while breathing through a mouthpiece. Minute ventilation (VE), tidal volume (VT), inspiratory time (TI), and total breathing cycle time (TT) were measured initially both spirometrically and from body surface displacements. When a mouthpiece was used, VE and breathing patterns were significantly altered during all activities such that VE, VT, and TT increased by 16, 34, and 20%, respectively. This mouthpiece effect was attenuated at the higher levels of VE. A task dependency of breathing pattern was also noted such that there was much greater variability of VT and TI for a given VE during the lifting activity compared with bicycling (coefficient of variation for VT of 0.39 +/- 0.09 vs. 0.20 +/- 0.07, P less than 0.01; and for TI of 0.38 +/- 0.08 vs. 0.21 +/- 0.08, P less than 0.01). We conclude that a mouthpiece significantly alters breathing pattern during varied types and intensities of activities, and breathing patterns may differ significantly from one activity to another. When the total dose of particulates inhaled in the lung are assessed, the mouthpiece effect and activity effect on breathing pattern must be considered.

Adult↗

PubMed1991

Absence of a hemidiaphragm: mechanical implications.

Respiratory system mechanics were evaluated in a 22-year-old asymptomatic man with absence of the left hemidiaphragm. We described changes in esophageal pressure (Pes), gastric pressure (Pga), chest wall configuration, and mediastinal motion during tidal breathing, breaths to total lung capacity (TLC), and Mueller maneuvers in the upright and supine position. We predicted that contraction of the single hemidiaphragm would drive the abdominal contents caudal on the side with the intact hemidiaphragm and displace the abdominal contents cephalad on the other side. This would drive the mediastinum toward the side with the intact diaphragm, thereby reducing its effectiveness in expanding the lung on that side. When upright, this effect would be minimized to the extent that the rib cage muscles lower pleural pressure in the thorax without the diaphragm. We found that (vital capacity) VC and TLC were greater upright than supine and that Pga deflections were almost as strongly negative as Pes deflections during upright quiet breathing and breaths to TLC. Thus the rib cage muscles enhanced the inspiratory action of the right hemidiaphragm in the upright position. In the supine position, Pes became negative without change of Pga during breaths to TLC and quiet inspirations. Here, contraction of the hemidiaphragm was the dominant mechanism generating the inspiratory pressure. During maximal Mueller efforts, the mediastinum shifted toward the side with the intact diaphragm in both positions and the maximum inspiratory pressures were low. These pressures were likely to have been limited by both the finite impedance to rotation of the thoracoabdominal contents or mediastinum and a mechanical disadvantage of the remaining hemidiaphragm. We conclude that the effectiveness of the single hemidiaphragm as an inspiratory pump requires passive impedance of the abdominal viscera and mediastinum and is enhanced in the upright position by the action of the rib cage muscles.

Adult↗

PubMed1990

Postural effects on measurements of tidal volume from body surface displacements.

Tidal volume measurements based on the sum of volume displacements of the rib cage (RC) and abdomen (Ab) are limited in accuracy when changes in posture occur. To elucidate the underlying sources of error, five subjects performed spinal flexion-extension isovolume maneuvers and then performed Konno-Mead isovolume maneuvers at different lung volumes while erect, with the spine fully flexed, and at intermediate degrees of spinal flexion. RC and Ab dimensions were measured with respiratory inductance plethysmograph belts, and spinal flexion was assessed by a pair of magnetometers measuring the xiphi-Ab distance (Xi). RC and Ab volume-motion coefficients (alpha and beta, respectively) were calculated from the slope (-beta/alpha) of the Konno-Mead isovolume lines. We found that 1) spinal flexion with constant lung volume mainly increases the RC dimension, thereby displacing the Konno-Mead isovolume lines, and 2) spinal flexion decreases the -beta/alpha by decreasing beta. The error related to displacement averaged 28.4 +/- 15% of vital capacity, whereas the error related to changes in beta averaged 14 +/- 6% (SD). The systematic relationship of these errors with the degree of spinal flexion provides a mechanism whereby the addition of Xi to RC and Ab displacements significantly (P less than 0.001) improves volume estimates.

Abdomen↗

PubMed1989

Relapse of Pneumocystis carinii pneumonia in the upper lobes during aerosol pentamidine prophylaxis.

Pneumocystis carinii pneumonia was diagnosed by bronchoalveolar lavage of the upper lobes in a patient with the acquired immunodeficiency syndrome (AIDS) receiving aerosol pentamidine prophylaxis. Serendipitous availability of a normal premorbid lung gallium scan indicated that pneumocystosis had developed during aerosol pentamidine prophylaxis; at the time of presentation a repeat gallium scan indicated disease limited to the upper lobes. The relation of this unusual form of isolated upper lobe Pneumocystis carinii pneumonia to aerosol pentamidine prophylaxis warrants further investigation.

Administration, Inhalation↗

PubMed1989

Preferential fatigue of the rib cage muscles during inspiratory resistive loaded ventilation.

Because the inspiratory rib cage muscles are recruited during inspiratory resistive loaded breathing, we hypothesized that such loading would preferentially fatigue the rib cage muscles. We measured the pressure developed by the inspiratory rib cage muscles during maximal static inspiratory maneuvers (Pinsp) and the pressure developed by the diaphragm during maximal static open-glottis expulsive maneuvers (Pdimax) in four human subjects, both before and after fatigue induced by an inspiratory resistive loaded breathing task. Tasks consisted of maintaining a target esophageal pressure, breathing frequency, and duty cycle for 3-5 min, after which the subjects maintained the highest esophageal pressure possible for an additional 5 min. After loading, Pinsp decreased in all subjects [control, -128 +/- 14 (SD) cmH2O; with fatigue, -102 +/- 18 cmH2O; P less than 0.001, paired t test]. Pdimax was unchanged (control, -192 +/- 23 cmH2O; fatigue, -195 +/- 27 cmH2O). These data suggest that 1) inability to sustain the target during loading resulted from fatigue of the inspiratory rib cage muscles, not diaphragm, and 2) simultaneous measurement of Pinsp and Pdimax may be useful in partitioning muscle fatigue into rib cage and diaphragmatic components.

Adult↗

PubMed1989

Oxygen cost of breathing during fatiguing inspiratory resistive loads.

When a subject breathes against an inspiratory resistance, the inspiratory pressure, the inspiratory flow, and the lung volume at which the breathing task takes place all interact to determine the length of time the task can be sustained (Tlim). We hypothesized that the mechanism actually limiting tasks in which these parameters were varied involved the rate of energy utilization by the inspiratory muscles. To test this hypothesis, we studied four experienced normal subjects during fatiguing breathing tasks performed over a range of pressures and flows and at two different lung volumes. We assessed energy utilization by measuring the increment in the rate of whole body O2 consumption due to the breathing task (VO2 resp). Power and mean esophageal pressure correlated with Tlim but depended also on lung volume and inspiratory flow rate. In contrast, VO2 resp closely correlated with Tlim, and this relationship was not systematically altered by inspiratory flow or lung volume. The shape of the VO2 resp vs. Tlim curve was approximately hyperbolic, with high rates of VO2 resp associated with short endurance times and lower rates of VO2 resp approaching an asymptotic value at high Tlim. These findings are consistent with a mechanism whereby a critical rate of energy utilization determines the endurance of the inspiratory pump, and that rate varies with pressure, flow, and lung volume.

Esophagus↗

PubMed1989

Dyspnea on immersion: mechanisms in patients with bilateral diaphragm paralysis.

Patients with bilateral diaphragm paralysis are able to inflate their lungs by two mechanisms: relaxing the abdominal wall or expanding the rib cage. Each maneuver promotes lung expansion by shifting support of the abdominal contents from the abdominal wall to the diaphragm. We describe a patient with bilateral diaphragm paralysis who experienced acute dyspnea when immersed in water to the level of the abdomen and discuss the precipitation of dyspnea in the context of the strategies available to these patients for lung inflation.

Abdominal Muscles↗

PubMed1989

Respiratory mechanics in acute quadriplegia. Lung and chest wall compliance and dimensional changes during respiratory maneuvers.

We measured lung and chest wall compliance as well as rib cage and abdominal dimensions in the supine position in five acute C4-7 quadriplegics. Studies were performed serially from 1 to 12 months after injury. Results were compared with those of control groups of chronic (greater than 1 yr after injury) quadriplegics and normal volunteers. We found that lung compliance was lower in acute and chronic quadriplegics (0.129 +/- 0.023 and 0.176 +/- 0.043 L/mm Hg, respectively) than in normal subjects (0.278 +/- 0.086 L/mm Hg) and that these changes apparently occurred within 1 month of injury. Specific lung compliance appeared to be reduced to a lesser degree, suggesting that the changes in lung compliance were partly due to reduced lung volumes and partly to altered mechanical properties of the lung. During respiratory maneuvers, abdomen and rib cage dimensional changes demonstrated rib cage distortion. This distortion was less severe in chronic than in acute quadriplegics. The improvement in chest wall stability was likely due to increased strength of cervical accessory muscles of respiration and improved coupling of the various rib cage elements in chronic quadriplegics.

Acute Disease↗

PubMed1989

Chest wall distortion in patients with flail chest.

Ventilators can impose resistive and elastic loads during subject-initiated and spontaneous breaths. Such loads might worsen the chest wall distortion that is characteristic of patients with flail chest. We have tested this expectation in nine patients with flail chest and four normal subjects. All subjects breathed for 3 to 5 min on each of the following modes: assist control, intermittent mandatory ventilation (IMV), continuous positive airway pressure 5 to 10 cm H2O by demand valve and by a high flow system (CPAP-HF), and spontaneously (T-piece). Pressure at the airway opening was evaluated as a measure of ventilator loading, and magnetometric displacements of the major chest wall dimensions were evaluated to assess chest wall distortion. In contrast to the normal volunteers, patients with flail chest displayed chest wall distortion during active inspirations. The patterns of distortion were variable among patients. The degree of distortion varied among ventilator modes; generally, there was a greater degree of chest wall distortion in breaths with greater loading. For example, distortion was greater during the spontaneous breaths taken on the IMV-mode than during spontaneous breaths taken on the T-piece. The CPAP-HF mode resulted in the least distortion, reversing chest wall distortion in five patients, improving it in two, and not changing the distortion in the remaining two. The improvements may be related to positive pleural pressures and to the minimal ventilator-imposed load of the high gas flow system. The distortion imposed by ventilators increases the work of breathing in these patients and may thus contribute to difficulty in weaning.

Aged↗

PubMed1988

Increased lung volume limits endurance of inspiratory muscles.

We examined the influence of lung volume on the ability of normal subjects to sustain breathing against inspiratory resistive loading. Four normal subjects breathed on a closed circuit in which inspiration was loaded by a flow resistor. Subjects were assigned a series of breathing tasks over a range of pressures and flows. In each task there was a specified resistor and also targets for either mean esophageal or airway opening pressure, respiratory frequency, and duty cycle. Endurance was assessed as the length of time to failure of the assigned task. The prime experimental variable was lung volume, which was increased by approximately 1 liter during some tasks; 8 cmH2O continuous positive airway pressure was applied to increase lung volume without increasing elastic load. As previously shown (McCool et al.J. Appl. Physiol. 60: 299-303, 1986), for tasks that could be sustained for the same time, there was an inverse linear relationship of mean esophageal pressure with inspiratory flow rate. This trade-off of pressure and flow was apparent both with and without the increase of lung volume. Comparable tasks, however, could not be sustained as long at the higher lung volumes. This effect of volume on endurance was greater for tasks characterized by high inspiratory pressures and low flow rates than for tasks that could be sustained for the same time but that had lower inspiratory pressures and higher flow rates. This is probably due to the effects of shortening of the sarcomere on fatiguability. Increased lung volume, per se, may contribute to respiratory failure because of increased inspiratory muscle fatiguability by mechanisms independent of elastic load.

Airway Resistance↗

PubMed1988

Effects of posture on stimulated ventilation in quadriplegia.

Quadriplegics are able to compensate for alterations of operational length of the diaphragm by reflexly increasing neural drive to the diaphragm. This increase in neural drive is adequate to maintain required tidal volume and minute ventilation during quiet breathing in these patients with limited inspiratory muscle function. It is not known, however, if this neural compensation is sufficient to preserve ventilation when the diaphragm is stressed by simultaneously changing its operational length and increasing ventilatory demands. This issue was explored in 7 quadriplegics whose vital capacity was reduced to 15 to 53% of predicted. The diaphragm was stressed by shortening its length from the supine to a 60 degree tilted position, and also by inducing hyperventilation by having the subjects rebreathe 7% CO2. Response to this stress was recorded by monitoring the ventilatory response to rebreathing CO2 (delta VE/delta PCO2), and also by measuring mouth pressure 0.1 s after occluding the airway at the start of inspiration during CO2 rebreathing (delta P0.1/delta PCO2). A change from the supine to the tilted position caused an increase in resting end-expiratory volume of 0.8 +/- 0.2 L (SD) and therefore shortened the diaphragm. Despite this shortening of diaphragm length and the stress of CO2 rebreathing, there was no significant change in delta VE/delta PCO2 and delta P0.1/delta PCO2 with changes in posture. The delta VE/delta PCO2 was 0.82 +/- 0.42 L/min/mm Hg supine versus 0.95 +/- 0.65 L/min/mm Hg when tilted. The delta P0.1/delta PCO2 was 0.18 +/- 0.08 cm H2O/mm Hg supine versus 0.20 +/- 0.10 cm H2O/mm Hg tilted.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Dioxide↗

PubMed1988

Respiratory muscle dysfunction in Parkinson's disease.

Patients with Parkinson's disease may have more difficulty performing repetitive motor acts than single motor acts because of bradykinesia and skeletal muscle rigidity. We thought that repetitive ventilatory tasks might be similarly limited and that this dysfunction would likely contribute to respiratory muscle fatigue. We studied 9 patients with Parkinson's disease who had no evidence of restrictive or obstructive lung disease and 5 normal age-matched control subjects who performed repetitive, forced inspiratory resistive-loaded tasks. The time a given mean airway opening pressure could be sustained, the incremental oxygen cost of breathing, and the work rate of breathing (W) were measured. Although maximal static inspiratory pressures were comparable in both groups, 8 of the 9 patients could not sustain as high a W in the resistive-loaded tasks as could the normal control subjects (41.0 +/- 23.0 versus 67.7 +/- 29.1 J/min; mean +/- SD, p less than 0.01) and the efficiency of breathing was reduced (2.0 +/- 0.8 versus 3.8 +/- 1.4%; p less than 0.01). These findings are similar to derangements of task performance by peripheral skeletal muscle groups in Parkinson's disease.

Aged↗

PubMed1988

Unilateral absence of the diaphragm in an asymptomatic adult.

An asymptomatic 22-year-old man was evaluated for a persistent left lower lobe infiltrate. Barium enema and upper gastrointestinal series revealed colon and small bowel freely mobile in the left thorax. CT confirmed absence of the left hemidiaphragm. This is the first reported case of total absence of a hemidiaphragm in an adult, and extends the clinical spectrum of diaphragmatic defects where strangulation of hernia contents may occur , the asymptomatic presentation of complete absence of the hemidiaphragm with the unimpeded movement of abdominal contents suggests that no treatment is necessary.

Adult↗

PubMed1987

Pathophysiology of cough.

Mucous secretions are normally removed by ciliary beating. When this defense mechanism is impaired or overwhelmed by increased secretions, cough then becomes an important means of secretion removal. For cough to be effective, the linear velocity of gas traveling through the airways should be high. Since the linear velocity of gas is related to flow and the cross-sectional area of the airways, cough is most effective when expiratory flows are great (effort independent) and dynamic compression (effort dependent) leads to a reduction of the cross-sectional area of the larger downstream airways. Cough failures may be related to either inadequate generation of expiratory flow rates (that is, in obstructive lung disease or inspiratory muscle weakness), failure to dynamically compress the airways (that is, in expiratory muscle weakness or increased collapsibility), alterations in airway geometry (that is, in bronchiectasis), or abnormal quantity or quality of mucous production (that is, in chronic bronchitis).

Cough↗