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Biomedical subjects

A F DiMarco

Publications and source records attributed to A F DiMarco.

At least 55 records · Page 3Linked to original sources
PubMed1989

Asthma in the pregnant patient: a review.

The occurrence of asthma during pregnancy is not an uncommon event and dictates specific treatment consideration. Proper management requires an understanding of the normal physiologic respiratory alterations during pregnancy, factors affecting maternal-fetal gas exchange, and use of drug therapy considered safe for both the mother and fetus. With optimum modern day therapy, a favorable outcome for both mother and fetus can be expected.

Adrenal Cortex Hormones↗
PubMed1988

Effect of amrinone on diaphragm blood flow.

The purpose of the present study was to examine the effect of amrinone, a drug known to augment cardiac output and dilate peripheral vascular beds, on diaphragm blood flow. Studies were performed on 12 anesthetized mechanically ventilated dogs in which strips of left costal diaphragm were developed in situ. Strip blood flow was assessed with a drop counter attached to a catheter tied into the phrenic veins' draining strips. Strip tension was measured with an isometric force transducer. Amrinone was administered as an intravenous bolus of 2 mg/kg followed by a continuous infusion of 25 micrograms.kg-1.min-1. Amrinone increased cardiac output and resting diaphragm blood flow [from 1.8 +/- 0.1 to 3.2 +/- 3 (SE) l/min and from 13 +/- 2 to 29 +/- 6 (SE) ml.100 g-1.min-1, respectively, P less than 0.001 for both comparisons]. Amrinone also increased blood flow during periods of rhythmic contraction (tension time indexes of 0.1-0.4, P less than 0.05 for comparisons of flow with and without amrinone at each tension time index) and increased the magnitude of the postcontraction hyperemia (P less than 0.02 for comparisons of hyperemic flow with and without amrinone at tension time indexes of 0.3 and 0.4). Graded occlusion of the inferior vena cava produced reductions in arterial pressure, cardiac output, and diaphragm blood flow both before and after amrinone. Both cardiac output and diaphragm blood flow were greater after amrinone, however, at all levels of blood pressure examined. These findings indicate that amrinone can override diaphragm vasoregulatory systems and augment diaphragm blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Amrinone↗
PubMed1987

Activation of the inspiratory intercostal muscles by electrical stimulation of the spinal cord.

Electrical stimulation of the spinal cord was evaluated as a method of activating the inspiratory intercostal muscles. Studies were performed in anesthetized dogs after hyperventilation-induced apnea. A stainless steel electrode, rubberized along its entire length except for 2 to 3 mm at the distal tip, was introduced epidurally onto the dorsal surface of the thoracic spinal cord. Stimulating electrodes were also placed in each hemidiaphragm. Intercostal electromyograms, inspired volume, and thoracoabdominal movements were monitored. The inspiratory capacity was determined in each animal as the volume required to achieve an airway pressure of +25 cm H2O during passive lung inflation. Spinal cord stimulation at the T2-T3 spinal level resulted in maximal inspired volume generation and electrical activation of the parasternal, external, and internal intercostal muscles of the upper and midrib cage regions as determined by electromyograms. Intrathoracic pressure swings increased progressively with increasing stimulus amplitude and frequency until plateaus were reached at 6 mA and 40 Hz, respectively. Postphrenicotomy spinal cord stimulation resulted in expansion of the rib cage and reduction in circumference of the abdominal compartment. Inspired volumes during spinal cord stimulation were 537 +/- 49 ml (prephrenicotomy, prone), 347 +/- 19.6 ml (postphrenicotomy, prone), and 303 +/- 30.6 ml (postphrenicotomy, supine). Bilateral diaphragm activation alone resulted in inspired volumes of 404 +/- 39 ml. Combined diaphragm and postphrenicotomy spinal cord stimulation (supine) resulted in an inspired volume of 712 +/- 72 ml, which approximated the inspiratory capacity (803 +/- 35 ml). Our results suggest that spinal cord stimulation may be a useful physiologic and clinical tool to produce coordinated contraction of the inspiratory intercostal muscles.

Animals↗
PubMed1987

Effects of intermittent negative pressure ventilation on respiratory muscle function in patients with severe chronic obstructive pulmonary disease.

The reduced respiratory muscle strength and increased work of breathing in patients with severe chronic obstructive pulmonary disease (COPD) may predispose these patients to the development of respiratory muscle fatigue and consequent respiratory failure. To test the hypothesis that these patients may be experiencing chronic respiratory muscle fatigue, we studied the effects of resting the respiratory muscles in a group of patients with severe COPD. Fifteen stable patients with severe COPD were randomized into study and control groups. In 8 study group patients (Group B), breathing was assisted with a negative pressure ventilator 3 to 6 h daily for 3 consecutive days. The remaining 7 patients served as controls (Group A) and did not receive any intervention. Baseline lung function was evaluated by spirometry and arterial blood gas determinations. Respiratory muscle strength and endurance were evaluated by maximal inspiratory and expiratory pressures (MIP and MEP, respectively) and the maximal duration that isocapnic hyperventilation equal to 50 and 70% of the 12-s maximal voluntary ventilation could be sustained (DSV). Baseline DSV was determined as the best effort of several practice trials. All measurements were repeated on the final day of assisted ventilation approximately 2 to 3 h after its discontinuation. After assisted ventilation, the DSV at 50 and 70% of the maximal voluntary ventilation improved significantly (p less than 0.05). Maximal inspiratory pressure and MEP increased to 114% (p less than 0.05) and 112% (p = 0.05) of baseline values, respectively. Mean arterial PCO2 in the hypercapnic subgroup of Group B patients decreased from 60 mm Hg before to 52 mm Hg after assisted ventilation (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Dioxide↗
PubMed1987

Management of chronic alveolar hypoventilation with nasal positive pressure breathing.

Negative pressure ventilation is the most common method of providing assisted ventilation without a tracheostomy. Unfortunately, negative pressure devices have several disadvantages and are not well tolerated by all patients. We present a patient in whom intermittent assisted ventilation was applied successfully by using a nasal mask to provide positive pressure ventilatory support.

Adult↗
PubMed1985

The effects of inspiratory resistive training on respiratory muscle function in patients with muscular dystrophy.

The effects of inspiratory resistive training on respiratory muscle function was evaluated in 11 patients with Duchenne, limb-girdle, and facio-scapulo-humeral (FSH) type muscular dystrophy. Muscle training consisted of breathing against an inspiratory resistance for two 15-minute sessions each day while at home. Following 6 weeks of training, there were significant increases in the maximum resistance that could be tolerated for at least 5 minutes (P < 0.01) and also in the maximum duration that ventilations equal to 30%, 50%, 70%, and 90% of the maximum voluntary ventilation could be sustained (P < 0.05). In six patients who trained for an additional 6-week period, respiratory muscle endurance increased even further. The degree of improvement in respiratory muscle endurance was positively correlated with baseline vital capacity (r = 0.84, P < 0.05) and maximal inspiratory pressure (r = 0.76, P < 0.05). Spirometry, functional residual capacity, and maximal inspiratory and expiratory pressures were not affected by training. We conclude that inspiratory resistive training improves respiratory muscle endurance in muscular dystrophy patients. Improvement in respiratory muscle function may serve to delay the onset of respiratory complications in patients with muscular dystrophy.

Adolescent↗
PubMed1985

Respiratory responses to ventilatory loading following low cervical spinal cord injury.

This study compared the respiratory responses to ventilatory loading in 8 normal subjects and 11 quadriplegic patients with low cervical spinal cord transection. Progressive hypercapnia was produced by rebreathing. Rebreathing trials were carried out with no added load and with inspiratory resistive loads of 5 and 16 cmH2O. l-1 X s. Measurements were made of ventilation and of diaphragmatic electromyographic activity. Base-line hypercapnic ventilatory responses were significantly lower than normal in the quadriplegic patients, but the effects of resistive loading on the ventilatory responses were comparable in the two groups. The change in peak moving-average diaphragmatic electrical activity (DI peak) for a given change in CO2 partial pressure (PCO2) and DI peak at PCO2 55 Torr increased significantly with resistive loading both in the normal subjects and the quadriplegic patients. In the normal subjects, but not in the quadriplegic patients, inspiratory duration increased progressively with increasing resistance. The increase in DI peak during ventilatory loading in the normal subjects was a consequence of inspiratory prolongation. In contrast, in the quadriplegic patients during breathing against the larger resistive load, there was a significant increase in the average rate of rise (DI peak divided by the time from onset to peak) of diaphragmatic activity. The change in DI rate of rise for a given change in PCO2 increased to 137 +/- 13% (SE), and the DI rate of rise at PCO2 55 Torr increased to 128 +/- 8% (SE) of control values. These results indicate that compensatory increases in diaphragmatic activation during ventilatory loading occur in quadriplegic patients in whom afferent feedback from rib cage receptors is disrupted.

Adolescent↗
PubMed1984

Effects of expiratory threshold loading on thoracoabdominal motion in cats.

Expiratory muscle activity may alter rib cage and abdominal configuration at end-expiration and thereby affect the pattern of thoracoabdominal motion during subsequent inspiration. In this study, expiratory muscles were stimulated by the application of a series of expiratory threshold loads (ETL) (range: 0 to + 10 cm H2O) in 10 cats lightly anaesthetized with pentobarbitone. Thoracoabdominal motion was monitored by inductance plethysmography. Peak internal intercostal and abdominal muscle electrical activity increased proportionately with the magnitude of the ETL, suggesting comparable activation of both expiratory muscle groups. Increases in end-expiratory abdominal volume, however, were greater than increases in end-expiratory rib cage volume, during ETL. This resulted in a shift of the end-expiratory thoracoabdominal position to the right of the relaxation characteristic. During ETL, there was inward movement of the abdomen in early inspiration and this decrease in abdominal volume correlated closely with the change in end-expiratory abdominal volume and the magnitude of the ETL (mean r = 0.95, P less than 0.01). In three animals, sectioning the abdominal muscles resulted in a further increase in end-expiratory abdominal volume for a given ETL. Deepening anesthesia progressively reduced and eventually abolished expiratory muscle activation and under these conditions, ETL increased end-expiratory rib cage and abdominal volume along the thoracoabdominal relaxation characteristic. The results of this study indicate that while abdominal muscle activation acts to decrease abdominal volume at end-expiration, the action of the expiratory intercostal muscles predominates during ETL to produce a smaller rib cage volume at the expense of an enlargement of abdominal volume.

Abdomen↗
PubMed1984

Sensation of respiratory force following low cervical spinal cord transection.

The psychophysical technique of magnitude scaling was used to assess the sensation of respiratory muscle force in patients with low cervical spinal cord transection. The exponents of the power function relationship between load magnitude and sensation intensity during graded elastic and resistive ventilatory loading in the quadriplegic patients were 0.51 and 0.54, respectively. These values were significantly lower than those in normal subjects (P less than 0.05). This impairment in load sensation could not be attributed to differences in either the duration or magnitude of the forces generated by muscles of inspiration during loading, since the power function relationships between airway pressure and sensation intensity corrected for inspiratory duration were also significantly lower in the quadriplegic patients compared with the normal subjects. In contrast the perception of respiratory force during inspiratory maneuvers against a closed airway, as determined by both magnitude estimation and production tests, was the same in normal subjects and quadriplegics. These results suggest that afferent signals from rib cage receptors are important in shaping the intensity of the sensation during submaximal ventilatory loading. During maximal loading, i.e., airway occlusion, when respiratory muscle tension changes proportionally with the motor command, centrally generated efferent command signals may be employed to subserve the sensation of respiratory muscle force when inputs from rib cage muscle receptors are not available.

Adult↗
PubMed1984

The flow-volume loop during glossopharyngeal breathing.

The flow-volume loops of three patients with chronic poliomyelitis were examined during glossopharyngeal breathing and compared with those during forced vital capacity maneuvers using only chest wall muscles. Peak expiratory flow rates and vital capacities were greater in all subjects after inspiration using glossopharyngeal breathing. During glossopharyngeal breathing, there was a progressive fall in the inspiratory flow rate and volume of each stroke as pulmonary volume increased.

Adult↗
PubMed1984

False-positive transbronchial needle aspiration in bronchogenic carcinoma.

In a patient with bronchogenic carcinoma, a transbronchial needle aspiration of subcarinal and paratracheal lymph nodes was performed for purposes of staging. On cytologic examination of the specimen, a clump of malignant cells was found; however, subsequent mediastinoscopy and thoracotomy showed no evidence of metastases to mediastinal lymph nodes. We postulate that specimens from transbronchial needle aspiration can be contaminated with tumor cells located on the airway surface epithelium.

Aged↗
PubMed1983

Immediate changes in ventilation and respiratory pattern associated with onset and cessation of locomotion in the cat.

In high decerebrate unanaesthetized cats (pre-collicular/pre-mamillary) which developed spontaneous co-ordinated locomotor activity, ventilation, breathing pattern, phrenic nerve, external and internal intercostal electromyogram (e.m.g.) activities were examined. Locomotion was also induced by electrical stimulation of the subthalamic locomotor region and in a few cases the mesencephalic locomotor region. Quadriceps muscle e.m.g. was used to monitor locomotor activity. Spontaneous locomotor activity was associated with an immediate increase in ventilation and shift of the ventilatory CO2 response curve to the left. Tidal volume was smaller and respiratory rate larger at any given level of ventilation during spontaneous locomotion. Increases in respiratory rate were due to reductions in both inspiratory and expiratory duration. Upon cessation of locomotion, these changes abruptly returned to control values. Within the first one or two walking steps of spontaneous locomotor activity, the rate of rise of phrenic activity increased slightly while peak phrenic activity remained relatively constant; peak internal intercostal activity increased markedly while peak external intercostal activity decreased. Similar changes in ventilation, phrenic, external and internal intercostal activities were observed in association with locomotion induced by stimulation within the subthalamic or mesencephalic locomotor regions. In contrast to spontaneous locomotor activity, however, increases in both external and internal intercostal activities were often observed. Peak amplitudes of both external and internal intercostal activities increased linearly with increasing levels of end-tidal PCO2 during rest and during locomotion. However, at any given level of PCO2 peak external intercostal activity was smaller and peak internal intercostal activity larger during locomotion than at rest. With increasing peak quadriceps e.m.g. activity at a constant walking rate, external intercostal activity was progressively inhibited while internal intercostal activity was progressively enhanced. No consistent change in peak phrenic activity was observed with changes in peak quadriceps activity. With increasing walking rate at a constant peak quadriceps e.m.g., peak phrenic and peak internal intercostal activities progressively increased and peak amplitude of external intercostal activity (which was inhibited below the activity observed at rest) also progressively increased. The virtually simultaneous changes in quadriceps activity and respiratory motor activities suggest that the increase in ventilation at exercise onset is neurally mediated. Furthermore, these results suggest that the motor pathways to both the spinal locomotor pattern generators and the pattern-controlling mechanisms for respiration are driven in parallel to provide a quantitative relationship between respiratory motor output and locomotor activity. The functional significance of the alterations in respiratory pattern and participation of the different respiratory muscles is discussed.

Animals↗
PubMed1983

Occlusion pressure and breathing pattern in patients with interstitial lung disease.

The ventilatory and occlusion pressure (P100) responses to hypercapnia, maximal inspiratory airway and transdiaphragmatic pressures, and the separate volume contributions of the rib cage and abdomen to tidal breathing were evaluated in 16 patients with chronic stable interstitial lung disease. Compared with those in the normal subjects, ventilation and P100 at a PCO2 = 55 mmHg were significantly higher (p less than 0.05 and p less than 0.01, respectively) in the patients with interstitial lung disease. However, the ventilatory and occlusion pressure responses to hypercapnia (delta VE/delta PCO2 and delta P 100/delta PCO2, respectively) were not significantly different between the groups. Maximal inspiratory airway pressure was significantly reduced in the patient group (p less than 0.05); maximal transdiaphragmatic pressure was also reduced but not significantly. At any given level of ventilation, tidal volume was decreased and breathing frequency increased in the patients with interstitial lung disease (p less than 0.05). The greater respiratory frequency was caused by reductions in both expiratory and inspiratory time. Because of smaller tidal volumes, rib cage expansion was reduced in the group of patients when compared with that in normal subjects during both spontaneous breathing and when compared at the same level of hypercapnia; abdomen volume was reduced to a lesser extent. We conclude that in patients with interstitial lung disease, non-chemical, presumably neural, mechanisms, increase respiratory drive and alter the breathing pattern. We speculate that both vagal mechanisms and mechanoreceptors in the chest wall sensitive to rib cage expansion contribute to these responses.

Adult↗
PubMed1982

Sensation of inspired volume in normal subjects and quadriplegic patients.

To investigate the influence of respiratory muscle tension and feedback from rib cage receptors, the sensation of inspired volume was compared in normal subjects and quadriplegic patients during active breathing, with and without the addition of an inspiratory resistive load, and during passive ventilation produced by a tank respirator. In separate trials, volume sensation was assessed using tests of magnitude estimation and volume reproduction. The mean exponents and standard errors for the magnitude estimation of inspired volume in normal subjects were 1.32 +/- 0.08, 1.24 +/- 0.06, and 1.23 +/- 0.09 during passive, active, and loaded breathing, respectively. These values were not significantly different from one another, nor were there any differences between normal subjects and quadriplegics. During volume reproduction trials where the mechanical conditions were different between control and test breaths, the inspired volumes during active unloaded breathing were significantly smaller than during passive ventilation but greater than the inspired volumes during loaded breathing. Errors in volume reproduction were no different in normal subjects and quadriplegics, suggesting that inputs from rib cage receptors are not essential for the sensation of inspired volume. The sensation of inspired volume in both normal subjects and quadriplegics was found to be unaffected by inhalation of a 2% lidocaine solution. This suggests that upper airway receptors are also not essential for volume sensation. The intensity of the sensation of a given inspired volume may depend on the level of the central nervous system motor command and/or on the tension developed by the diaphragm.

Adult↗
PubMed1981

Positive feedback facilitation of external intercostal and phrenic inspiratory activity by pulmonary stretch receptors.

Both in lightly pentobarbitone anesthetized and decerebrate cats increments in lung volume (V) during inspiration caused facilitation of inspiratory activity both in phrenic (Phr) and external intercostal (EI) motoneurons. This effect had low volume threshold, well below eupnoeic tidal volumes. It was readily reduced or abolished by small additional doses of pentobarbitone. This facilitatory effect appeared with considerably greater magnitude in EI than in Phr. The response magnitude was linearly related to the corresponding increments in V but not to increments in airflow (V). Sustained elevation of V at zero V caused sustained facilitation of EI and Phr. This positive feedback facilitation which was similarly obtained in spontaneously breathing and paralysed cats occurred continuously with great regularity in every breath. It was abolished by bilateral vagotomy but could then be elicited by electrical stimulation of the central end of the vagus nerve at the same threshold strengths required to elicit a just detectable shortening of inspiratory duration. The results indicate that the slowly adapting pulmonary stretch receptors are responsible for this positive feedback facilitation prior to the negative feedback effect on the inspiratory 'off-switch' elicited by the same receptors. Clear distinctions are described between the reflex characteristics of this 'low-threshold' volume dependent facilitatory reflex and the 'high-threshold' transient excitatory reflex effects provoked by large and rapid inflations.

Animals↗