Expiratory muscle activity during pulmonary edema in the anesthetized dog

The present study evaluated the reflex response of the expiratory muscles to pulmonary congestion and edema. The electromyograms of two thoracic and four abdominal expiratory muscles were recorded in 12 anesthetized dogs. Pulmonary edema was induced by rapid saline infusion in six dogs and injection of oleic acid into the pulmonary circulation in the remaining six dogs. Both forms of pulmonary edema reduced pulmonary compliance, interfered with gas exchange, and induced a rapid and shallow breathing pattern. The electrical activity of all abdominal muscles was suppressed during both forms of pulmonary edema. In contrast, the electromyogram activity of the thoracic expiratory muscles was not significantly affected by pulmonary edema. Acute pulmonary arterial hypertension produced in two dogs by inflating a balloon in the left atrium had no effect on ventilation or expiratory muscle electrical activity. In two vagotomized dogs, pulmonary edema did not inhibit the expiratory muscles. We conclude that pulmonary edema suppresses abdominal but not thoracic expiratory muscle activity by vagal reflex pathway(s). Extravasation of fluid into the lung appears to be more important than an increase in pulmonary vascular pressure in eliciting this response.

Catabolism of calcitonin gene-related peptide and substance P by neutral endopeptidase

Calcitonin gene-related peptide (CGRP) and substance P (SP) are released from sensory nerves upon exposure to irritating stimuli. Neutral endopeptidase (NEP), a membrane-bound peptidase, cleaves many peptides including SP, thereby limiting their biological actions. Recombinant NEP cleaved CGRP1 approximately 88-fold less rapidly than it cleaved SP. The slow cleavage by NEP of CGRP compared to SP suggests that this enzyme is likely to have weaker physiologic effects on CGRP than have been demonstrated for SP.

Reflex effect of esophageal distension on respiratory muscle activity and pressure

The electrical activity of the respiratory skeletal muscles is altered in response to reflexes originating in the gastrointestinal tract. The present study evaluated the reflex effects of esophageal distension (ED) on the distribution of motor activity to both inspiratory and expiratory muscles of the rib cage and abdomen and the resultant changes in thoracic and abdominal pressure during breathing. Studies were performed in 21 anesthetized spontaneously breathing dogs. ED was produced by inflating a balloon in the distal esophagus. ED decreased the activity of the costal and crural diaphragm and external intercostals and abolished all preexisting electrical activity in the expiratory muscles of the abdominal wall. On the other hand, ED increased the activity of the parasternal intercostals and expiratory muscles located in the rib cage (i.e., triangularis sterni and internal intercostal). All effects of ED were graded, with increasing distension exerting greater effects, and were eliminated by vagotomy. The effect of increases in chemical drive and lung inflation reflex activity on the response to ED was examined by performing ED while animals breathed either 6.5% CO2 or against graded levels of positive end-expiratory pressure (PEEP), respectively. Changes in respiratory muscle electrical activity induced by ED were similar (during 6.5% CO2 and PEEP) to those observed under control conditions. We conclude that activation of mechanoreceptors in the esophagus reflexly alters the distribution of motor activity to the respiratory muscles, inhibiting the muscles surrounding the abdominal cavity and augmenting the parasternals and expiratory muscles of the chest wall.

Integration of cardiorespiratory responses in the ventrolateral medulla

Interventions confined to the region adjacent to the VMS can produce both respiratory and circulatory effects. Although it has been suggested that both breathing and vasomotor changes arise from the same neural elements near the VMS, our own investigations indicate that the neurons involved are closely linked but not identical. This belief is supported by recent studies which show that AII and angiotensin antagonists microinjected into the rostral portion of the VMS can significantly modify blood pressure and respiration but can produce effects of different sign. These observations, coupled with previous studies of the VMS, indicate the possibility that regions near the VMS may contribute to integration of circulatory and respiratory responses.

Comparison of the effects of hypercapnia on phrenic and hypoglossal activity in anesthetized decerebrate and decorticate animals

To examine the effects of suprapontine structures on the activity of hypoglossal and phrenic nerves, 13 chloralose anesthetized, paralyzed (gallamine triethiodide) and artificially ventilated cats were studied. In all animals vagi and carotid sinus nerves were cut bilaterally. All animals were first hyperventilated to apnea and then made progressively hypercapnic by rebreathing under hyperoxic conditions. Following midcollicular decerebration, the peak phasic activity of the hypoglossal nerve was significantly depressed and the PCO2 at which apnea occurred (apneic point) increased. However, following high decerebration or decortication the activity of the hypoglossal nerve was increased at higher CO2 levels and there was no change in apneic point. By contrast, peak phrenic nerve activity was not altered by any of the above surgical procedures. Neither systemic blood pressure nor respiratory frequency were significantly altered by these procedures. The results indicate that suprapontine structures can appreciably modify hypoglossal activity.

Elevated blood lead in a population near a lead smelter in Kosovo, Yugoslavia

A survey of residents of a community surrounding a lead smelter has revealed an alarming incidence of elevated blood lead and erythrocyte protoporphyrin concentrations. In particular, children who were less than 3 yr of age were severely affected. Of those children tested in December, 1980, 35% had blood lead concentrations between 50-69 microgram/dl, while an additional 12% had concentrations greater than or equal to 70 microgram/dl, and are, therefore, at risk for severe neurological sequelae.

Decreased pulmonary pressor response to acute hypoxia in chronically hypoxic rats

The pulmonary vascular response to an acute hypoxic stimulus was examined in rats which were kept for 4 weeks in a hypoxic environment and compared to that of rats kept in a normoxic environment. To this end, the effects of breathing gas mixtures containing 7, 21 an 100% O2 on right ventricular systolic pressure (RVPs), cardiac output (Q) and calculated pulmonary vascular resistance (PVR) in chronically hypoxic (CH) rats and rats kept in a normoxic environment (N) were examined. During breathing of 21% O2 RVPs, Q, and PVR were all higher in CH than in N rats. Breathing a gas mixture containing 7% O2 had no effect on systemic blood pressure, heart rate or Q, in both CH and N rats. When compared to breathing of 21% O2, the RVP and PVR remained unchanged in CH rats breathing 7% O2, while both variables significantly (p less than 0.01) increased in N rats. The presented data indicate that the reaction of the pulmonary vasculature to an hypoxic challenge is decreased in CH rats.