PubMed Health⌕ Search

Biomedical subjects

A Krishnan

Publications and source records attributed to A Krishnan.

72 records · Page 4Linked to original sources
PubMed1987

Arterial to end-tidal carbon dioxide tension difference during anaesthesia for tubal ligation.

Twenty-nine patients scheduled for postnatal tubal ligation by minilaparotomy under general anaesthesia were studied. Arterial and end-tidal carbon dioxide tensions were determined during anaesthesia. The mean arterial to end-tidal carbon dioxide tension difference was 0.08 kPa (SEM 0.05). Thirty-one percent of the patients had negative values. These results were similar to those observed during Caesarean section. The physiological changes responsible for reduced arterial to end-tidal carbon dioxide values, persist into the postnatal period. It is predicted from the regression analysis of the time between delivery and anaesthesia for tubal ligation and arterial to end-tidal CO2 difference, that the values might return to normal nonpregnant levels by 8 days following delivery.

Adult↗
PubMed1986

Flow requirements for the Bain breathing circuit during anaesthesia for caesarean section.

We studied the relationship between arterial carbon dioxide tension (PaCO2) and fresh gas flow (FGF) during use of the Bain breathing circuit for Caesarean section anaesthesia. Thirty-one patients undergoing Caesarean section were anaesthetised using the Bain circuit with intermittent positive pressure ventilation. The PaCO2 were measured at FGF of 70 ml X kg-1 X min-1, 80 ml X kg-1 X min-1, and 100 ml X kg-1 X min-1. The FGF requirement to maintain a given PaCO2 during Caesarean section anaesthesia is the same as the requirements for nonpregnant subjects, despite the increase in carbon dioxide production associated with pregnancy. This is probably because the total FGF determined by body weight and given during Caesarean section anaesthesia is 15-20 per cent higher than nonpregnant levels, due to the weight gain associated with pregnancy. A FGF of 100 ml X kg-1 of pregnant weight/min maintains PaCO2 of 4.44 kPa predelivery, which is in the desirable range of PaCO2 during Caesarean section.

Adult↗
PubMed1986

Cat lung hemodynamics: comparison of experimental results and model predictions.

Commonly, attempts have been made to learn about the structure and function of the pulmonary vascular bed from measurements of arterial and venous pressures and blood flow rate under steady-state conditions (e.g., from pressure vs. flow data) or dynamic conditions (e.g., from vascular occlusion data). Zhuang et al. (J. Appl. Physiol. 55: 1341-1348, 1983) have presented a detailed model of steady-state cat lung hemodynamics based on direct measurements of anatomical and elasticity data. This model provides an opportunity to better understand the information content of the hemodynamic data. Therefore, in the present study we carried out a series of steady-state and dynamic experiments on isolated cat lungs. We then compared the results with those predicted by the model. We found that the model provided a good fit to the steady-state data. However, to fit the dynamic data, some modifications were necessary to account for the viscous behavior of the vessel walls and to move the first moment of the distribution of vascular resistance toward the arterial end of the vascular bed relative to that of the distribution of vascular compliance. Due to the sensitivity of the vascular resistance to small changes in vessel diameters and branching ratio, the modifications in morphometry represent small changes in morphometric data and are probably within the range of uncertainty in such data. The modifications had little effect on the steady-state model simulations but substantially improved the dynamic model simulations, suggesting that the dynamic data are quite sensitive to small changes in the relative distributions of vessel diameters and elasticity.

Animals↗
PubMed1986

On-demand nalbuphine for post-operative pain relief.

Twenty-five patients with moderate to severe pain after major upper abdominal surgery chose to receive nalbuphine on demand from a Cardiff Palliator for pain relief. An initial i.v. injection of nalbuphine 20 mg was followed by 5 mg given over 90s in response to each successful demand. A maximum of 20 doses (100 mg) hr-1 of nalbuphine was available, plus additional bolus doses. Twelve patients obtained good pain relief and completed the 5 hour observation period. 13 patients withdrew from the study, 8 because of inadequate pain relief and 2 because of side-effects. At least half the patients who complained of inadequate pain relief at the time had no subsequent memory of the events. Despite high dosage in some cases (up to 200 mg in an hour) no clinically important cardiovascular or respiratory effects were observed.

Adult↗
PubMed1985

Controlled comparison of nalbuphine and morphine for post-tonsillectomy pain.

A controlled investigation was conducted to compare the effectiveness of morphine and nalbuphine in the prevention of pain and restlessness after tonsillectomy in children. Sixty children between 4 and 12 years old were randomly allocated to receive intramuscular morphine 0.2 mg/kg, nalbuphine 0.3 mg/kg or no medication approximately 5 minutes before the conclusion of surgery. Pain and restlessness were assessed 1 and 2 hours after injection, and side effects were recorded. The assessments were made double-blind. Both nalbuphine and morphine decreased restlessness and pain 1 hour (p less than 0.01) and 2 hours (p less than 0.05) after surgery. No significant differences were found between the two groups of patients who received opioids. Both nalbuphine and morphine caused more drowsiness than placebo 2 hours after surgery (p less than 0.001). Other side effects were uncommon. Nalbuphine may offer advantages compared with morphine in regard to safety and convenience of use for the treatment of post-tonsillectomy pain in children.

Child↗
PubMedDate not supplied

Craniovertebral junction tuberculosis: a review of 29 cases.

PURPOSE: The purpose of this work was to describe the various imaging findings in craniovertebral tuberculosis and the importance of imaging in treatment in these patients. METHOD: A retrospective review of MR and CT scans in 29 patients with craniovertebral tuberculosis was performed. The images were reviewed, paying special attention to both bony (skull base, atlas, and axis) and soft tissue involvement in addition to atlantoaxial dislocation, lateral subluxation of the dens, and compression of the spinal cord. RESULTS: Suboccipital pain with neck stiffness was the most common presenting symptom in our patients. The skull was involved in 19 of the 29 cases, clivus involvement was seen in 11 patients, and occipital condyle involvement was present in 14 patients. Detailed analysis of atlas involvement due to tuberculosis showed the lateral masses to be predominantly affected. The dens was involved in 18 cases (62%). Soft tissue masses in the prevertebral area were seen in 22 patients, paravertebral in 27 patients, and epidural involvement in 25 patients was identified. Atlantoaxial displacement was present in seven cases, lateral mass-dens subluxation in five, and superior subluxation of the dens through the foramen magnum compressing the medulla was seen in two cases. Spinal cord compression with intrinsic cord changes was noted in 12 cases. All patients received multidrug antituberculous therapy for 1 year. The presence of neurologic deficit and instability of the atlantoaxial complex was pivotal in further management in these patients. CONCLUSION: A high degree of clinical suspicion is necessary when confronted with patients with neck stiffness and tenderness over the upper cervical vertebrae. MRI in these patients provides a sensitive method for the diagnosis of craniovertebral tuberculosis.

Abscess↗
PubMedDate not supplied

Binaural interaction in the human frequency-following response: effects of interaural intensity difference.

The binaural interaction component (BIC) of the 500-Hz human frequency-following response (FFR) was evaluated as a function of interaural intensity difference (IID) using a lateralization paradigm. The robust FFR interaction component (FFR-BIC) was shown to decrease systematically with increasing IID with no discernible FFR-BIC for IID values larger than about 20 dB. These findings are similar to that observed for the high-frequency auditory brainstem response interaction component (ABR-BIC). Thus, like the ABR-BIC, the FFR-BIC may be correlated with binaural fusion and the perceived location of the fused image of the sound. These results taken together suggest that the binaural neurons in the brainstem are able to utilize IID cues presented in both low-frequency and high-frequency sounds.

Adolescent↗
PubMedDate not supplied

Human frequency-following responses to two-tone approximations of steady-state vowels.

Auditory nerve single-unit population studies have demonstrated that phase-locking plays a dominant role in the neural encoding of the spectrum of speech sounds. Since the scalp-recorded human frequency-following response (FFR) reflects synchronous, phase-locked activity in a population of neurons in the rostral auditory brainstem, it was reasoned that the human FFR might preserve information about certain acoustic features of speech sounds. FFRs to three different two-tone approximations of vowels (symbols, see text) were obtained from 10 normal-hearing human adults at 85, 75, 65 and 55 dB nHL. Spectrum analyses of the FFRs revealed distinct peaks at frequencies corresponding to the first and the second formants across all levels suggesting that phase-locked activity among two distinct populations of neurons are indeed preserved in the FFR. Also, the FFR spectrum for vowels (symbols, see text) revealed a robust component at 2F1-F2 frequency suggesting that the human FFR contains a neural representation of cochlear nonlinearity. Finally, comparison of FFRs to the vowel approximations and the individual components at F1 and F2 revealed effects that may be suggestive of two-tone synchrony suppression and/or lateral inhibition. These results suggest that the scalp-recorded FFR may be used to evaluate not only neural encoding of speech sounds but also processes associated with cochlear nonlinearity.

Adolescent↗
PubMedDate not supplied

Human frequency-following response: representation of tonal sweeps.

Auditory nerve single-unit population studies have demonstrated that phase locking plays a dominant role in the neural encoding of steady-state speech sounds. Recently, we have reported that the phase-locked activity underlying the human frequency-following response (FFR) could also encode the first two formants of several tonal approximations of steady-state vowels. Since auditory nerve single-unit population studies have also demonstrated that phase locking is used to represent time-varying speech-like sounds, it was reasoned that the phase-locked neural activity underlying the human FFR, likewise, is dynamic enough to represent time-varying sounds. FFRs to a rising and a falling tone were obtained from 8 normal-hearing adults at 95, 85, 75 and 65 dB nHL. Results clearly demonstrated that the human FFR does indeed follow the trajectory of the rising and falling tones. Also, amplitude changes in the FFR supported the view that neural phase locking decreases with increasing frequency. Finally, the relatively smaller FFR amplitude for the falling tone compared to its rising counterpart lends further support to the notion that rising tones produce greater neural synchrony than falling tones. These results indicate that the human FFR may be used to evaluate encoding of time-varying speech sounds like diphthongs and certain consonant-vowel syllables.

Adolescent↗
PubMedDate not supplied

Spontaneous isolated lesser sac hematoma in a patient with hemophilia.

In patients with hemophilia, hematomas in the mesentery and bowel wall have been described uncommonly. The lesser sac is a rare site of spontaneous hemorrhage even in patients with bleeding diathesis; only a single case of isolated lesser sac hemorrhage has been reported in a hemophiliac patient. We report a similar case with no history of trauma. He recovered with administration of factor VIII concentrate.

Child↗
PubMedDate not supplied

Pedunculated nasal glioma: MRI features and review of the literature.

Nasal gliomas are uncommon lesions, with approximately 100 cases reported in the literature. We present a case of intranasal glioma with a pedicle of glial tissue and defect in the cribriform plate of the ethmoid bone. Presence of such a pedicle is almost always present in the encephaloceles and is known to be distinctively uncommon in nasal gliomas.

Glioma↗
PubMedDate not supplied

Imaging features of gossypiboma: report of two cases.

Recognition of postoperatively retained foreign body referred euphemistically as gossypiboma is essential but is very often considerably delayed. Legal implications as well as confusing configuration patterns cause considerable dilemma in the accurate diagnosis. We present computed tomographic features of gossypiboma in two patients who presented with symptoms of fever and pain in the immediate post-operative period. A prospective radiological diagnosis is essential for further management in these patients.

Adult↗
PubMedDate not supplied

Ruptured intracranial dermoids: magnetic resonance imaging.

Rupture of intracranial dermoids tumour is rare and carries with it the risk of significant morbidity as well as fatality. Three cases that presented with varying symptoms ranging from headache to chiasmatic compression and suspected to have rupture of dermoid tumour are described. The importance of MR imaging in their diagnosis is discussed.

Adult↗
PubMedDate not supplied

MR imaging in children with ectopic pituitary gland and anterior hypopituitarism.

Posterior pituitary ectopia refers to an absent normal posterior pituitary bright spot within the sella with ectopic bright signal at another site (such as the median eminence) on a weighted magnetic resonance. We describe two children with idiopathic anterior hypopituitarism who showed an ectopic posterior pituitary and absent pituitary stalk on imaging. We emphasize the association of the absent pituitary stalk in ectopic pituitary gland and low growth hormone levels.

Child↗
PubMedDate not supplied

Hallervorden Spatz disease: MR imaging.

Three patients were diagnosed as suffering from Hallervorden Spatz disease, a rare disorder, on the basis of their clinical and MRI findings.

Adult↗