Effect of isoflurane anaesthetic time on ocular a-scan ultrasonography measures and their relationship to age and OCT measures in the Guinea pig.

A-scan ultrasonography enables precise measurement of internal ocular structures. Historically, its use has underpinned fundamental studies of eye development and aberrant eye growth in animal models of myopia; however, the procedure typically requires anaesthesia. Since anaesthesia affects intra-ocular pressure (IOP), we investigated changes in internal ocular structures with isoflurane exposure and compared measurements with those taken in awake animals using optical coherence tomography (OCT). Continuous A-scan ultrasonography was undertaken in tri-coloured guinea pigs aged 21 (n = 5), 90 (n = 5) or 160 (n = 5) days while anaesthetised (up to 36 min) with isoflurane (5% in 1.5L/min O2). Peaks were selected from ultrasound traces corresponding to the boundaries of the cornea, crystalline lens, retina, choroid and sclera. OCT scans (Zeiss Cirrus Photo 800) of the posterior eye layers were taken in 28-day-old animals (n = 19) and compared with ultrasound traces, with choroid and scleral thickness adjusted for the duration of anaesthesia based on the changes modelled in 21-day-old animals. Ultrasound traces recorded sequentially in left and right eyes in 14-day-old animals (n = 30) were compared, with each adjusted for anaesthesia duration. The thickness of the cornea was measured in enucleated eyes (n = 5) using OCT following the application of ultrasound gel (up to 20 min). Retinal thickness was the only ultrasound internal measure unaffected by anaesthesia. All other internal distances rapidly changed and were well fitted by exponential functions (either rise-to-max or decay). After 10 and 20 min of anaesthesia, the thickness of the cornea, crystalline lens and sclera increased by 17.1% and 23.3%, 0.4% and 0.6%, and 5.2% and 6.5% respectively, whilst the anterior chamber, vitreous chamber and choroid decreased by 4.4% and 6.1%, 0.7% and 1.1%, and 10.7% and 11.8% respectively. In enucleated eyes, prolonged contact of the cornea with ultrasound gel resulted in an increase in thickness of 9.3% after 10 min, accounting for approximately half of the expansion observed in live animals. At the back of the eye, ultrasound measurements of the thickness of the retina, choroid and sclera were highly correlated with those from posterior segment OCT images (R2 = 0.92, p = 1.2 × 10-13, R2 = 0.55, p = 4.0 × 10-4, R2 = 0.72, p = 5.0 × 10-6 respectively). Furthermore, ultrasound measures for all ocular components were highly correlated in left and right eyes measured sequentially, when each was adjusted for anaesthetic depth. This study shows that the depth of ocular components can change dramatically with anaesthesia. Researchers should therefore be wary of these concomitant effects and should employ adjustments to better render 'true' values.

[Physiological characteristics and cardiac electrophysiology manifested in Minnesota coding of the "desert people" in Taklimakan Desert: study of 224 cases].

OBJECTIVE: To study the physiological characteristics and cardiac electrophysiology of the "desert people" in Taklimakan Desert, an isolated population of Uygurs. METHODS: Two hundred and twenty-four out of the 1030 "desert people", 133 males aged 37.8 +/- 17.5 (15-99) and 91 females aged 34.1 +/- 12.1 (27-85), underwent measurement of height, body weight, waist circumference, and blood pressure. Twelve-lead resting electrocardiogram was obtained and Minnesota coding was conducted. 150 Kariya Uygurs, 76 males aged 50.7 +/- 15.6 (27-85) and 75 females aged 46.6 +/- 11.7 (24-69) were used as controls. RESULTS: The abnormal Minnesota coding rate in the "desert people" as a whole was 46.0%, significantly higher than that of the controls (35.1%, P < 0.05). In the "desert people", the abnormal Minnesota coding rate was 54.9% in the males, significantly higher than that in the females (33.0%, P < 0.05). In the control group, the abnormal coding rate was 28.0% in the females and 42.1% in the males. The ECG high left R amplitude rate (code 3-1, 3-3) of the "desert people" as a whole was 32.6%, significantly higher than that of the controls (12.6%, P < 0.001). Within the "desert people" group, the ECG high left R amplitude rate of the females was 19.8%, significantly lower than that of the males (41.2%, P < 0.005). Within the control group, the ECG high left R amplitude rate of the females was 10.7%, not significantly different from that of the males (14.5%, P > 0.5). The hypertension rate of the "desert people" was 7.6%, significantly lower than that of the controls (36.4%, P < 0.005). The hypertension rate of the "desert people" coded as with left high R amplitude was 12.2%, significantly lower than that of the controls coded as with left high R amplitude (41.6%, P < 0.005). The overweight and obesity rate of the "desert people" was 9.6%, significantly lower than that of the controls (23%, P < 0.005). The arrhythmia (8-1 - 8-8) rate of the "desert people" was 8.92%, not significantly different from that of the controls (6.62%, P > 0.05). The incidence of conduction block (7-1 - 7-8) of the "desert people" was 3.12%, not significantly different from that of the controls (2.64%, P > 0.05). CONCLUSION: The higher incidence of ECG high left R amplitudes and low prevalence of hypertension in the "desert people" suggest that the high left R amplitude in "Desert people" may be related to their thin chest wall, low BMI, and physiological left ventricular hypertrophy. The "desert people" have more physical work, and less stress and pollution. They have low incidence of congenital heart disease, rheumatic heart disease and hypertension. All these may be associated with a low incidence of arrhythmia.