Biomedical subjects

V Chernick

Publications and source records attributed to V Chernick.

At least 109 records · Page 6Linked to original sources

PubMed1975

Site of central chemosensitivity in fetal sheep.

The heart rate, blood pressure, and respiratory response to topically applied cyanide on the ventrolateral medullary surface and upper spinal cord was studied on exteriorized sinaortic-denervated fetal lambs under pentobarbital anesthesia. On all sites tested cyanide produced a rapid increase in heart rate and blood pressure (P smaller than 0.05) which was most pronounced from the area adjacent to the nerve roots IX to XI (mean 32%). Respiratory efforts consisting of 1-8 gasps were induced in half the applications to the medulla but never when the pledgets were applied to the spinal cord. The mean delay to response was 43 s (range 13-102 s). After cautery of the chemosensitive areas, topical application of cyanide failed to stimulate gasping, whereas intravenous cyanide or cord clamping still produced a vigorous respiratory response. It is concluded that sympathetic stimulation of the heart and blood vessels can originate centrally in response to local histotoxic hypoxia of the ventral medulla and upper spinal cord. Furthermore, it is proposed that in the apneic fetus histotoxic hypoxia of the medulla initiates respiration possibly by stimulating a special gasping mechanism which is separate from the respiratory center responsible for rhythmic breathing after birth. The responsible neurons must be located at least 2 mm beneath the ventral medullary surface.

Administration, Topical↗

PubMed1975

Electrical activity of phrenic nerve and diaphragm in utero.

Phrenic nerve activity, diaphragmatic EMG, and tracheal or pleural pressure changes were recorded in a chronic fetal sheep preparation. Three patterns of fetal phrenic nerve activity were observed: 1) a single burst; 2) irregular nonrhythmic bursts; and 3) prolonged rhythmic activity, seen only prior to fetal death. The total recording time was 54.53 h and the total duration of phrenic nerve activity was 65.34 min (2.16%). When an inactive period was defined as the absence of phrenic nerve activity for 60 s or more, active periods occupied 44.7% of the total time. Phrenic nerve activity was present in all fetuses and 97.5% of the time was coupled with diaphragmatic EMG. Both diaphragmatic EMG and intrapulmonary pressure changes occurred in the absence of phrenic nerve activity. In three fetal animals both phrenic nerves were transected. Tracheal pressure changes were seen which were not coupled with corresponding intrauterine pressure changes. Thus, changes in fetal tracheal pressure or diaphragmatic EMG do not necessarily represent the output of the fetal respiratory center. This study suggests that the fetal respiratory center is active in utero, but this activity is minimal and has a different pattern that that present after birth.

Animals↗

PubMed1975

Effect of metopirone on the synthesis of lung surfactant in does and fetal rabbits.

The possible role of endogenous corticosteroids in the induction of synthesis of lung surfactant in both maternal and fetal rabbits was investigated. Metopirone (SU 4885), which specifically inhibits B hydroxylation in the adrenal gland, thus preventing endogenous cortisol production was used in this study. Pregnant rabbits received one of four treatment regimens: saline, metopirone, cortisone or metopirone plus steroid for 6 days before delivery. Studies of the lungs of the adult rabbits revealed that lung weights and percent dry weight were not influenced by drug injection. However, lung DNA content (mg/g) in the metopirone-treated group was higher than the control group, indicating an increase in cell number. Compared to the saline-treated group there was a significant decrease in lung phospholipid content in the other three groups (p smaller than 0.005). A decrease in lung lecithin and phosphatidylethanolamine was also noted in these three groups indicating that the inhibition was in the early steps of biosynthesis of lung lecithin. The specific activity of 14C-labelled palmitate in lung lecithin was not altered by drug treatment indicating that saturated fatty acid incorporation into lung lecithin is not influenced by metopirone, steroid or a combination of both drugs. Quasi-static deflation pressure-volume characteristics of the lung were also similar in all groups. However, lungs of animals receiving both metopirone and steroid had a small but statistically significant decrease in minimum surface tension (p smaller than 0.05). The change in surface tension did not correlate with a change in lung retractive forces or with lung lipid content and was, therefore, of dubious biological significance. Metopirone administration to pregnant rabbits did not alter surface active properties in the fetus from the 26th to the 29th day of gestation when compared to control fetuses. At day 30-31 gestation the offsprings of metopirone-treated rabbits had lung total phospholipid and lecithin contents, and deflation pressure-volume curves similar to control group, but minimum surface tension of minced lung extracts were high in about 60% of the fetal lungs studied (p smaller than 0.05). These results suggest that endogenous steroid production may play a significant role in the maturation of the fetal lung.

Animals↗

PubMed1975

Bronchopulmonary dysplasia and lung rupture in hyaline membrane disease: influence of continuous distending pressure.

Review of 158 patients with hyaline membrane disease was undertaken. The introduction of artificial ventilation with a positive end-expiratory pressure (IPPB and PEEP) has doubled the prevalence of pneumothorax, pneumomediastinum and interstitial emphysema from 20.7% to 39.7%). Continuous negative distending pressure during spontaneous ventilation (CNP) was associated with a prevalence of lung rupture similar to that occurring spontaneously (4.8%). No patient treated with CNP alone developed bronchopulmonary dysplasia. Patients treated with IPPB with PEEP had a marked decreased prevalence of bronchopulmonary dysplasia (17.2%) when compared to patients treated with IPPB alone (36.2%), probably related to the enhanced overdistension of relatively normal areas of the lung may be related to the increased prevalence of lung rupture seen during IPPB with PEEP.

Humans↗

PubMed1974