Biomedical subjects

J Hortop

Publications and source records attributed to J Hortop.

5 recordsLinked to original sources

PubMed1989

Developmental effects of hypoxia and indomethacin on distribution of vascular resistances in lamb lungs.

The influence of postnatal age on the distribution of vascular resistances was studied in in situ, isolated, blood perfused lungs of lambs aged 6-12 h, 2-4 d, 2 wk, and 1 mo. The pressure gradients across the upstream, downstream, and compliant middle segments were determined by an inflow-outflow occlusion technique during mild hyperoxia (FIO2 = 0.28) and severe hypoxia (FIO2 = 0.04) under control and indomethacin-treated conditions. The greatest response to hypoxia was seen in the middle segment. A lesser, but significant response was also seen in the upstream segment. Indomethacin accentuated the hypoxic response of the total circuit and the middle segment at all ages, and the upstream segment in the two younger age groups. An age-dependent increase in total hypoxic reactivity was seen in control lungs, but not in indomethacin-treated lungs. When the pressure gradient across the middle segment alone was considered, an age-dependent increase in hypoxic reactivity was seen in controls and a decrease was seen in indomethacin-treated lungs. In contrast there were no age-dependent changes in the hypoxic responses of the upstream or downstream segments. These data suggest that the predominant site of hypoxic pulmonary vasoconstriction and dilator prostaglandin activity lies within the middle gradient in newborn lamb lungs. Furthermore, the age-dependent changes in the hypoxic response of the middle gradient appear to be altered by the modulating influence of dilator prostaglandins.

Aging↗

PubMed1988

The mechanical effects of expiratory airflow limitation on cardiac performance in cystic fibrosis.

The influence of altered lung mechanics on cardiac performance in cystic fibrosis (CF) was examined in an analysis of cardiorespiratory performance during exercise. The stroke volume (SV) response to exercise, derived from an indirect Fick (CO2) determination of cardiac output during submaximal steady-state exercise served as the index of cardiac performance. The relationship between exercising SV and forced expiratory volume in one second (FEV1), inspiratory duty cycle during exercise (Tl/Ttot) and exercising systemic arterial oxygen tension (PaO2) was examined in 15 studies involving 11 individuals with CF. The subjects were 12 to 25 yr of age and the FEV1 ranged from 15 to 72% predicted. Although a relationship existed between the SV expressed as a percentage of the mean predicted from height and gender (SV%) and PaO2 (r = 0.61, p less than 0.02), a more striking relationship was noted between SV% and either FEV1 or Tl/Ttot (r = 0.79 and 0.73, p less than 0.002). A multiple regression analysis of SV% identified an element of the relationship between FEV1 or Tl/Ttot and cardiac performance which was distinct from the influence of the coexisting hypoxia (p less than or equal to 0.05). The limitation in the SV response to exercise was noted to be in part reversible, coincident with an improvement in ventilatory mechanics that had occurred in 2 of the 4 persons in whom repeated studies were available. These observations suggest that in individuals with CF and a moderately severe degree of expiratory airflow limitation, there is a mechanical element of cardiopulmonary interdependence.

Adolescent↗

PubMed1987

Group B streptococcal sepsis in the piglet: effects of fluid therapy on venous return, organ edema, and organ blood flow.

We investigated the physiologic effects of normal saline versus 5% albuminated saline fluid resuscitation on 10-12-day-old piglets infected with group B streptococci for four hours. After intravenously receiving 1 X 10(10) bacteria/kg over 45 minutes, one group was untreated while the two fluid-treated groups received enough intravenous fluid to maintain the baseline cardiac output. An increase in the resistance to venous blood return was the major limitation to cardiac output. The resistance nearly quadrupled in the untreated piglets as shown by a 50% decrease in cardiac output with a nearly doubling of the driving pressure for venous return (mean circulatory pressure was normal and atrial pressures decreased by 70%). In both fluid-treated groups, resistance doubled as shown by an unchanged cardiac output with a doubling of the driving pressure (mean circulatory pressure increased by 50%) and atrial pressures remained at baseline). Blood volume was 9% below control in the untreated group and 13% above control in both fluid-treated groups. Much more crystalloid (155 ml/kg) than colloid (58 ml/kg) was necessary to maintain baseline cardiac output; this resulted in a 36% decrease in the plasma protein oncotic pressure of the former group and a 15% increase in the oncotic pressure of the latter group. Organ edema formation (ileum, pancreas, kidney, adrenal gland, lung) occurred only in the saline-treated animals. We conclude that increased resistance to venous return was the primary cause of shock in our model and that this can be effectively treated by giving enough intravenous fluid to elevate the mean circulatory pressure. However, if the plasma protein oncotic pressure is also lowered (saline group), organ edema results.

Acid-Base Equilibrium↗

PubMed1986

Cardiovascular involvement in osteogenesis imperfecta.

While aortic root dilatation and valvular dysfunction have been well-documented in osteogenesis imperfecta (OI), the nature and extent of cardiovascular involvement in OI have not been clearly delineated. A clinical and echocardiographic survey involving 109 individuals with various nonlethal OI syndromes from 66 separate families was undertaken. Clinically discernible valvular dysfunction was encountered in only four of the 109 individuals (aortic regurgitation in two, aortic stenosis in one, and mitral valve prolapse in one), none of whom were related. Aortic root dilatation was recognized echocardiographically in eight (12.1%) of 66 individuals comprising a subset of the sample in which each family was represented by a single individual. The extent of the aortic root dilatation was mild (the largest dimension measuring 4.3 cm) and was unrelated to the age of the individual. Dilatation was seen in each of the different OI syndromes but was strikingly segregated within certain families (p less than .001). In the same subset of 66 individuals, mitral valve prolapse was encountered in two or 6.9% of the 29 individuals aged 15 years or greater in whom adequate studies were obtained. This observed frequency was not different from that seen in a normal adult population. Aortic root dilatation appears to represent a distinct phenotypic trait in patients with OI that is nonprogressive and occurs in about 12% of affected individuals. Whether mitral valve prolapse should be considered as a part of the cardiovascular phenotype in OI, or alternately segregates as an independent autosomal dominant trait has yet to be determined.

Adolescent↗

PubMed1982

The effect of digoxin on exercise capacity and exercising cardiac function in cystic fibrosis.

The ability of digoxin to increase exercise capacity and stroke volume (SV) during exercise was evaluated in ten patients with cystic fibrosis (CF) ages 12 to 20 years with moderate to severe degrees of airway obstruction but no history of heart failure. A double-blind crossover trial of digoxin versus placebo was carried out. An evaluation of exercise performance was undertaken upon entry into the study, and after each of the one-week periods in which digoxin 0.25 mg/day or placebo was taken. Exercise testing consisted of a progressive exercise test on a cycle ergometer to measure maximum work capacity (Wmax) and a steady state test at 2/3 of the baseline Wmax. During the steady state test, the oxygen consumption and carbon dioxide production were measured and cardiac output (Q) was calculated by the indirect Fick (CO2) method. From Q and heart rate (HR), SV was derived. After digoxin, Wmax was unchanged. On steady state exercise HR was unchanged, but there was a slight but significant fall in Q due to a fall in SV. The decrease in SV was associated with exercising hypoxemia. We conclude that digoxin did not increase exercise capacity or improve exercising cardiac function in patients with moderate to severe airway obstruction due to CF.

Adolescent↗