Biomedical subjects
B M Corcoran
Publications and source records attributed to B M Corcoran.
Effect of vagotomy and vagal cooling on bronchoconstrictor response to substance P in sheep.
The bronchoconstrictor effect of intravenous substance P can be antagonised by atropine pre-treatment in several species, and we have previously reported this finding in anaesthetised sheep. In the present study, we have assessed the effect of cooling the right vagus after sectioning the left vagus (n = 6), and bilateral vagotomy (n = 7) on the bronchoconstrictor response to a single intravenous dose of substance P (SP) (0.3-1.0 mumol/kg) in anaesthetized female sheep aged 6 to 12 months. Respiratory parameters including tidal volume, flow and transpulmonary pressure pressure were measured, from which pulmonary resistance (RL; cmH2O.1(-1).s) and dynamic compliance (CDyn; ml.cmH2O(-1) were calculated. Systemic arterial pressures were also measured. Vagal cooling significantly attenuated the bronchoconstrictor response to SP at 7 degrees C (RL P < 0.01; Cdyn P < 0.001). A further reduction in the response to SP occurred at 3 degrees C, but this was not statistically significantly different from the response at 7 degrees C. Vagotomy abolished the response to SP. SP caused mild, but statistically insignificant, hypotension (119.7 vs. 107.7 mmHg). These results suggest SP causes bronchoconstriction in the anaesthetised sheep by vagal reflex mechanisms, involving stimulation of myelinated nerve fibre endings.
Feline asthma syndrome: a retrospective study of the clinical presentation in 29 cats.
Feline asthma syndrome (FAS) is a clinical condition characterised by recurrent bouts of coughing, wheezing and, or, dyspnoea. While the aetiology is unproven, the condition is believed to involve a type I immediate hypersensitivity reaction to inhaled allergens. In this paper the clinical data from 29 cats, where a diagnosis of FAS was made, are assessed retrospectively. The most common clinical presentation was recurrent bouts of coughing (n = 26) and dyspnoea (n = 21). Radiographic changes were noted in 24 cats, which included increased bronchial (n = 5), interstitial (n = 7) and mixed (n = 12) (bronchial and interstitial) patterns. Right middle lung lobe collapse was noted in two cats. Abnormal bronchial cytology was present in 16 cats. A predominant eosinophilic sample was collected in only three cats. There were minimal changes in differential white cell counts, and mild eosinophilia was found in only five cats. Prednisolone alone was the most effective therapy, although avoidance of putative aeroallergens and antibacterial therapy was effective in some. On the basis of the data from these cases it would appear that the diagnosis of FAS depends largely on the clinical presentation and radiographic findings. The value of ancillary tests in the diagnosis of FAS appears to be limited.
Age-related respiratory responses to substance P in normal sheep.
The in vivo effects of substance P (SP) on respiratory parameters in four different age groups of sheep were examined. Intravenous SP (10(-8) to 5 x 10(-6) mol kg-1 bodyweight) caused a dose-dependent reduction in dynamic compliance and increase in respiratory resistance in all four groups. The bronchoconstrictor response was age-related, with the greatest response occurring in the youngest age group (four to six months). In the oldest group (over four years) there was minimal bronchomotor response to SP, but a dose-dependent apnoea was present. These findings indicate that there is an age-related alteration in the respiratory response to SP in sheep.
Chronic tracheobronchial syndrome in eight dogs.
Chronic tracheobronchial syndrome was diagnosed in eight dogs which had had a chronic mild cough for two to 13 months but were otherwise clinically normal. In five of them there was evidence of contact with other coughing dogs before the appearance of clinical signs and the majority at first responded favourably to antibacterial therapy. The coughing occurred mainly when the dogs pulled on their leads or became excited. Three cases had bronchoscopic evidence of active airway inflammation, and five had varying numbers of inflammatory cells (neutrophils) in bronchial aspirates. There was no evidence of excessive production of mucus in the airways of any of the dogs. Seven had an increased bronchial pattern on radiographs but only one of the dogs has developed chronic bronchitis.
The effect of tachykinins on sheep bronchomotor tone.
The mammalian tachykinin neuropeptides substance P (SP) and neurokinin A (NKA) are present in the airways of several species and are involved in control of bronchomotor tone. We investigated the effect of SP and NKA on various respiratory and cardiovascular parameters in anaesthetized sheep. Dose-dependent decrease in dynamic compliance (Cdyn) and increase in respiratory resistance (RL) occurred with intravenous administration of SP. The predominant effect of NKA was on Cdyn with little or no effect on RL. Consequently SP is a more potent bronchoconstrictor than NKA in the sheep and affects both central and peripheral airway tone. The sensitivity to SP and NKA and the order of potency found suggests the NK-1 receptor predominates in sheep airways. Atropine and the ganglion blocker hexamethonium markedly reduced the bronchoconstriction caused by SP. SP and NKA were equipotent in causing a significant reduction in respiratory rate. SP caused a fall in mean blood pressure while NKA caused mild vasoconstriction. Neither peptide affected heart rate. We concluded that SP is a more potent bronchoconstrictor than NKA in the sheep and that the mechanism of action is mainly indirect involving modulation of postganglionic cholinergic nerve endings.
Effects of general anaesthesia on static respiratory compliance in dogs.
The effect of anaesthesia on total, pulmonary and chest wall static respiratory compliance was investigated in healthy spontaneously breathing dogs undergoing orthopaedic surgery. Total compliance fell by 26 per cent from the baseline measurement within 25 minutes of the first measurement (P less than 0.01), while pulmonary and chest wall compliances fell by 34 per cent and 40 per cent, respectively (P less than 0.01). Pulmonary compliance ceased to fall after 50 minutes, but chest wall compliance was still declining after 70 minutes. The decline in compliance could be prevented by periodic full lung inflation, with a significant difference being found between inflated and uninflated dogs (P less than 0.01). The reduction in compliance during anaesthesia is believed to be a consequence of reduced functional residual capacity and the development of lung tissue atelectasis.
Post traumatic tracheal stenosis in a cat.
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Peak mean myocardial velocities and velocity gradients measured by color M-mode tissue Doppler imaging in healthy cats.
We sought to assess the feasibility of recording the myocardial velocity gradients (MVGs) and mean myocardial velocities (MMVs) measured by color M-mode tissue Doppler imaging (TDI) in the free wall of unsedated normal cats (n = 18) with a 7.4-MHz probe equipped to record TDI images. The peak MVG and MMV values during the different phases of the cardiac cycle corresponded to certain color velocity patterns occurring in the left ventricular free wall (LVFW). Biphasic shifts were recorded in the tracings of both the MVG and MMV during early diastole (E1 and E2) as well as during the isovolumic relaxation (IVR) and isovolumic contraction (IVC) phases. Stepwise regression analysis showed that age was the only significant predictor for the peak MVG values during the 2nd phase of early diastole (E2) (r = -0.79, r2 = 0.63, and P < .001). The peak late diastolic MVG values were associated positively with age (r = 0.50, r2 = 0.25, and P < .05). The peak MMV values showed a negative association with age during E2 (r = -0.71, r2 = 0.50, and P < .001) as well as during early systole (Se) (r = -0.55, r2 = 0.30, and P < .05) and late systole (SI) (r = -0.62, r2 = 0.39, and P < .01). A positive association was found between age and the peak MMV values during late diastole (r = 0.54, r2 =- 0.29, and P < .05). The MVG values showed cyclic variations consistent with wall thickness changes. The accuracy of velocity determination and the spatial resolution of the system used were validated with a phantom. To our knowledge, this study is the 1st report of the application of this technique to the myocardium of cats,providing insights into the physiology of myocardial motion. It provides reference ranges of the peak MVG and MMV values for future studies of feline myocardial diseases.
Pulsed tissue Doppler imaging in normal cats and cats with hypertrophic cardiomyopathy.
Myocardial motion was quantified in normal cats (n = 25) and cats with hypertrophic cardiomyopathy (HCM) (n = 23) using the pulsed tissue Doppler imaging (TDI) technique. A physiologic nonuniformity was documented in the myocardial motion of normal cats, which was detected as higher early diastolic velocities, acceleration, and deceleration in the interventricular septum compared with the left ventricular free wall (LVFW). HCM cats exhibited lower early diastolic velocities, acceleration, and deceleration and also prolonged isovolumic relaxation time compared with normal cats. These differences were detected mainly along the longitudinal axis of the heart. A cutoff value of E' in the LVFW along the longitudinal axis >7.2 cm/s discriminated normal from HCM cats with a sensitivity of 92% and a specificity of 87%. The physiologic nonuniformity of myocardial motion during diastole was lost in affected cats. Systolic impairment (decreased late-systolic velocities in most segments along the longitudinal axis and decreased early systolic acceleration in both mitral annular sites) was evident in HCM cats irrespective of the presence of left ventricular outflow tract obstruction and congestive heart failure. Postsystolic thickening was recorded in the LVFW along the longitudinal axis only in affected cats (n = 6) and was another finding indicative of systolic impairment in the HCM of this species. This study identified both diastolic and systolic impairment in cats with HCM compared with normal cats. The study also documents the normal physiologic nonhomogeneity in myocardial motion in cats and the subsequent loss of this feature in the HCM diseased state.