Comparison of first, second, and third versus the average of six probe-corneal touches for intraocular measurement of two rebound tonometers in healthy horses.

The aim of this study was to evaluate the intraocular pressure (IOP) measurements obtained from first, second, and third probe-cornea touch (PCT) and compare them with the average of six PCTs using two rebound tonometers in horses. This study enrolled a total of thirty-eight stallions, comprising of 24 Arabian horses and 14 cross-breeds (with an average age of 8 ± 3 years). The IOP measurements of first, second, and third, as well as the average of six PCTs were obtained using either Tonovet (TV) or Tonovet Plus (TV+) rebound tonometers. The mean differences (95% limits of agreement) between the average of six PCTs and the first, second, and third PCTs were 0.1 (-4.8 to 5), 0.2 (-4.8 to 4.5), and 0.2 (-3.6 to 4.0) mmHg with TV, respectively. With TV+, the differences were 0.3 (-6.6 to 7.2), 1.1 (-8.6 to 10.8), and -0.2 (-3.6 to 4.0) mmHg, respectively. Compared to the average of six PCTs, only 89.5%, 92.1%, and 97.4% of IOP measurements obtained from TV and 78.9%, 73.3%, and 65.8% of IOP measurements obtained from TV+ were within 4 mmHg of the average of six PCTs for first, second, and third PCTs, respectively. In conclusion, the measurement of IOP in the first PCT achieved best agreement with the IOP measurement of six average PCTs. Therefore, the first PCT could be considered as an alternative option for measuring IOP in horses when obtaining an average of six PCTs is not feasible.

Comparison of intraocular pressure in New Zealand White rabbits measured using rebound and applanation tonometers and four different methods of physical restraint.

AIMS: To compare intraocular pressure (IOP) measurements obtained in rabbits using rebound (TV) and applanation (TPV) tonometers with four different methods of physical restraint. METHODS: A total of 20 New Zealand White rabbits (40 eyes) were included in this study. IOP readings were obtained from both eyes using the two different tonometers. The rabbits were placed on a table and restrained by wrapping in a cloth (Method I), by scruffing with rear support (Method II), by wrapping in a cloth and cupped in the hands (Method III), or by a box restrainer (Method IV). RESULTS: The mean IOP measurement obtained by TPV was higher than that obtained with the TV for all handling methods. Mean differences (TV-TPV, in mmHg) in IOP were -5.3 (95% Cl = -6.5 to -4.1) for Method 1, -4.7 (95% Cl = -6.2 to -3.29) for Method II, -4.9 (95% Cl = -6.2 to -3.7) for Method III and -7.6 (95% Cl = -9.2 to -5.9) for Method IV. Using the TV tonometer, mean IOP for Method IV was higher than for Method I (mean difference 2.1 (95% Cl = 1.1-3.1)), whereas using the TPV tonometer, mean IOP for Method IV was significantly higher than Method I, II, and III (mean differences: 4.4 (95% Cl = 2.6-5.9), 3.7 (95% Cl = 2-5.3) and 3.8 (95% Cl = 2-5.4), respectively). According to Bland-Altman plots, IOP readings for TPV tended to be higher than those for TV with all handling methods, but with a lack of agreement. The mean difference and 95% limits of agreement for the differences between TV and TPV were -5.4 mmHg (-12.5-1.9 mmHg), -4.7 mmHg (-12.9-3.5 mmHg), -4.9 mmHg (-12-2.2 mmHg), and -7.5 mmHg (-17.4-2.3 mmHg), with Methods I, II, III, and IV, respectively. Comparing TV and TPV, only 7.5%, 12.5%, 27.5%, and 15% of IOP measurements from 20 rabbits were within the range considered clinically acceptable for IOP (± 2 mmHg) for Method I, II, III, and IV, respectively. CONCLUSION AND CLINICAL RELEVANCE: In conclusion, the physical restraint method should be recorded when IOP is measured in rabbits, and TV and TPV tonometers cannot be used interchangeably (high bias and low proportion of measurements within ± 2 mmHg).

The agreement of rectal temperature with gingival, ocular and metacarpal pad temperatures in clinically healthy dogs.

AIMS: To compare alternative methods of recording body temperature (BT) with rectal temperature (RT) in clinically healthy dogs. METHODS: This prospective study included 97 healthy mixed-breed dogs (43 females and 54 males). The gingival temperature (GT) was collected by using a human non-contact, infrared forehead thermometer, while ocular temperature (OT) and metacarpal pad temperature (MPT) were obtained with an infrared thermal camera. The degree of agreement was determined using the Bland-Altman method, with RT considered as the reference temperature. RESULTS: A total of 382 readings were obtained from four different anatomical regions. The mean difference and their 95% limits of agreement for the differences between RT-GT, RT-OT, and RT-MPT were 0.18°C (-0.95°C-1.32°C), 0.79°C (-0.45°C-2.04°C), and 0.50°C (-0.63°C-1.62°C), respectively. The GT, OT, and MPT values were within ±0.5°C of RT for 65.9%, 19.5%, and 52.5% of dogs, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Although GT, OT, and MPT were a quick way to estimate BT in dogs, these measurements were not comparable with RT. The GT measurement achieved the best agreement with RT measurement (lowest bias and the highest proportion of measurements within ±0.5°C). The GT could be considered an option for monitoring changes to body temperature in clinically healthy dogs where RT measurement is not possible.

Utility of P300 auditory event related potential latency in detecting cognitive dysfunction in growth hormone (GH) deficient patients with Sheehan's syndrome and effects of GH replacement therapy.

OBJECTIVE: Impaired cognitive function has been demonstrated in adults with growth hormone (GH) deficiency (GHD) by using different neuropsychological tests. Despite several studies, present knowledge about the impact of GHD and GH replacement therapy (GHRT) on cognitive function is limited. P300 event-related potential (ERP) application is a well-established neurophysiological approach in the assessment of cognitive functions including the updating of working memory content and the speed of stimulus evaluation. GHD is a well-known feature of Sheehan's syndrome and cognitive changes due to GHD and the effects of GHRT remain to be clarified. The present study was designed to investigate the effects of GHD and 6 months of GHRT on cognitive function in patients with Sheehan's syndrome by using P300 latency. DESIGN AND METHODS: The study comprised 14 patients with Sheehan's syndrome (mean age, 49.5+/-7.8 years) and 10 age-, education- and sex-matched healthy controls. With hormone replacement therapy, basal hormone levels other than GH were stable before enrollment and throughout the GHRT. The diagnosis of GH deficiency was established by insulin-tolerance test (ITT), and mean peak level of GH in response to insulin hypoglycemia was 0.77+/-0.35 mIU/l. Treatment with GH was started at a dose of 0.45 IU (0.15 mg)/day in month 1, was increased to 0.9 IU (0.30 mg)/day in month 2 and was maintained at 2 IU (0.66 mg)/day. Initially baseline auditory ERPs in patients and controls were recorded at frontal (Fz), central (Cz), and parietal (P3 and P4) electrode sites. In the patient group, ERPs were re-evaluated after 6 months of GH replacement therapy. During each session P300 amplitude and latency were measured. RESULTS: Mean serum insulin-like growth factor-I (IGF-I) concentration in the patient group before GHRT was 23+/-13 ng/ml. After 6 months of GH therapy mean IGF-I significantly increased to an acceptable level, 234+/-71 ng/ml (P<0.05). The mean latencies (at all electrode sites) of the patients before GHRT were found to be significantly prolonged when compared with those of normal controls (P<0.05). After 6 months of GHRT mean P300 latencies (at all electrode sites) were decreased significantly when compared with latencies before treatment (P<0.05). CONCLUSIONS: The present study, using P300 ERP latencies, therefore suggests an impairment of cognitive abilities due to severe GHD in patients with Sheehan's syndrome and an improvement of cognitive function after 6 months of physiological GHRT. Moreover, this was a novel application of P300 ERP latencies in cognitive function detection in patients with GHD. Further studies with different patient groups need to be done to assess the clinical use of this electrophysiological method in the diagnosis of cognitive dysfunction due to GHD.

Habituation of the auditory evoked potential in a short interstimulus interval paradigm.

The present experiment was carried out to investigate elicitation and habituation of the auditory event related potentials with stimulus trains utilizing a short interstimulus intervals (ISI) of 1500 ms. Scalp event related potentials elicited by auditory stimuli were recorded in 10 male subjects. Thirty auditory stimuli were presented binaurally over headphones to every subject with a duration of 1000 ms, each with a constant ISI of 1500 ms. No task relevance was given to the stimuli. Wave-forms were collected using a Pentium 100 computer. All analyses were carried out over the 30 trials. In each single trial event related potentials, latencies and amplitudes of N1-P2 components were analyzed separately for four frequency bands (0.3-70, 0.3-4, 4-7, 7-13 Hz). Trend effects were tested with linear-regression analyses (N1-P2 amplitude x stimuli number). We found that the amplitude from the first stimulus decreased reliably across trial blocks of the N1-P2 components and that it was directly affected by ISI. The relevance of these results for the habituation is discussed.

The effect of sex differences on event-related potentials in young adults.

Female/male cognitive differences have been studied for some time; however, such differences in Turkish population is unknown. Evoked potentials (EPs) of the brain have been applied as an index of information processing in a wide variety of normal and cognitive impaired subjects. Scalp event-related potentials (ERP) evoked by auditory stimuli were recorded in 20 male and 18 female neurologically and audiologically normal young Turkish subjects of 18-25 years (Av. 20.6) of age. Standard auditory "Oddball" paradigm involving simple discrimination task of concentrating on infrequent (target) stimulus and ignoring frequent (non-target) stimulus was employed. EEG activity was recorded at the Fz, Cz, Pz and Oz electrode sites of the 10-20 system using Ag/AgCl electrodes. Wave forms were collected and averaged off-line by a Pentium 100 computer, which also controlled the stimulus presentation. In general, significant main effects of gender and electrode site on evoked potential components were found. The interpeak amplitudes N1-P2 and N2-P3 were higher in the male subjects than in the female subjects at Cz. N2-P3 were higher in the male subjects than in the female subjects at Oz. The latencies of N1, P2, N2, P3 components were not different between both sex. For both sexes we found that N1-P2 amplitude was higher at Fz and Cz than Pz and Oz. N2-P3 amplitude was higher at Fz than Oz for only female subject. In male subjects, latency of N2 was longer at Fz than Oz. There were no significant differences in the latencies of N1, P2, and P3 components between electrode sites in both sexes. We suggest that ERP components could be affected by sex, electrode site, and cognitive performance.

Zinc-induced alterations in contractile properties of rat diaphragm muscle in vitro.

The effect of zinc ions on the isometric contraction of rat diaphragm muscles in the presence and in the absence of external calcium was studied. Using a transducer, the isometric force was measured as a function of supramaximal electrical stimulation, either directly or indirectly applied to the muscle. The following parameters were measured: peak twitch tension, PT, twitch contraction time, CT, relaxation half-time, RT-1/2, and peak rates of tension increase and decrease, +dP/dt and -dP/dt. The following zinc-induced alterations were observed: an increase of the PT; a decrease of the RT-1/2; an increase in the +dP/dt and -dP/dt. The CT was not changed significantly. Our results suggest that zinc ions have a positive inotropic effect on isolated diaphragm muscle. The increase in PT may be explained by a zinc-activated Ca2+ uptake by sarcoplasmic reticulum. This was followed by an increase in the rate of rise of tension development, which was secondary to increased -dP/dt. The mechanism(s) by which extracellular Ca2+ contributes to this action of zinc is not known.

Dependence of fatigue properties on the pattern of stimulation in the rat diaphragm muscle.

Diaphragm fatigue was studied in isolated phrenic nerve diaphragm strips from 28 Swiss Albino rats. Three procedures were used to estimate the isometric twitch characters and force frequency responses to fatigue of the rat diaphragm at different rates of phrenic nerve stimulation. Diaphragm fatigue was induced by using low frequency stimulation (0.2 ms pulse duration, at 5 Hz frequency, 3 min), high frequency stimulation (0.2 ms pulse duration, at 50 Hz frequency, 3 min), and by production brief submaximal contraction (25 Hz, for 160 ms at the rate of 1/s for 45 contractions). Tension was reduced to 26.67 +/- 5.10% and 6.59 +/- 2.64% and 68.69 +/- 2.45% of the initial value at the end of the low and high frequency and brief submaximal stimulation, respectively. In all the fatigue experiments, twitch tension and tetanic tension decreased, contraction and 1/2 relaxation time prolonged and force-frequency curves shifted to the right. The most significant changes were observed in low frequency fatigue whereas the most moderate ones were recorded in brief submaximal fatigue. It was concluded that fatigue in the rat diaphragm depended on the frequency and duration of stimulation as well as on the number of stimuli delivered to the muscle. Various mechanisms of muscle fatigue are described in the discussion to explain the observations made in the present investigation.

Rat diaphragm muscle contraction with and without oxygen enrichment.

We investigated the effect of deprivation of oxygen circulation in the organ bath on the tension generation of the diaphragm in vitro. Adult male Swiss Albino rats were quickly killed and the left hemidiaphragms removed. Isolated phrenic nerve-diaphragmatic strip preparations were placed in an individual organ chamber containing Krebs solution and were connected to a force displacement transducer. The solution was maintained at 32 degrees C and bubbled with 95% O2-5% CO2. For the measurement of isometric twitch characteristics, supramaximal voltage was delivered via phrenic nerve electrodes. After turning off the gas circulation, isometric twitch characteristics were determined at 5, 10, 15, and 20 minutes. Then the muscle was allowed to recover under aerobic conditions (i.e., while bathed in a fresh solution, gassed with 95% O2-5% CO2). The isometric contractile properties were determined at the same intervals. In spite of no change in contraction time (CT) and relaxation time (1/2 RT), twitch amplitude (Pt) decreased following the termination of oxygen circulation (p < 0.05). The twitch tension improved in the recovery period but the decrease of tension developed more rapidly than the increase of tension development. We suggest that the decrease in the twitch tension was possibly due to a direct effect of intracellular acidosis. This study shows that no important change occurred in Ca+2 release and/or in the uptake in the sarcoplasmic reticulum, because of the finding of the CT and 1/2 RT values.

The effects of theophylline and caffeine on the isolated rat diaphragm.

It is a well known fact that theophylline enhances the force of diaphragmatic contraction and delays fatigue. The action of caffeine which is a methylxanthine analogue on skeletal muscle are complex. It was claimed in few studies that the caffeine was more effective on the diaphragmatic contractility than the theophylline. The aim of this study is to compare the effects of theophylline and caffeine on the tension generated by fresh and fatigued diaphragmatic muscle. Studies were performed in vitro on diaphragmatic muscle strips of rats activated by electrical stimuli applied via the phrenic nerve. Isometric twitch characteristics (twitch tension, contraction and 1/2 relaxation time) were measured. Force-frequency responses were generated using twitches and tetanic contractions produced by stimulating the phrenic nerve with 0.2 ms pulses at 10, 20, 50 and 100 Hz for 1 s with 30 s intervals. Moderate fatigue was then induced by repeated submaximal contractions (25 Hz, 160 ms, at the rate of 1/s for 45 contractions). In fresh muscle 1 mM theophylline and 1 mM caffeine increased diaphragmatic tension 40.98 +/- 8.50% and 82.30 +/- 12.21% of the initial value respectively. Theophylline did not alter contraction time but prolonged 1/2 relaxation time, whereas caffeine had no effect on any one. Theophylline induced force production in all frequencies. Caffeine caused an increase in force only in < 20 Hz, but a decrease in 50 and 100 Hz. In brief submaximal fatigue, both 1 mM theophylline and 1 mM caffeine partly prevented fatigue (effect of caffeine was more potent). This study suggests that caffeine has a greater effect than theophylline on the muscle. Possible mechanism(s) of action of theophylline and caffeine on diaphragmatic contractility and fatigue were discussed. It may well be the fact that they might have different mechanisms of action on the isolated rat diaphragm.

Effect of acute starvation on rat diaphragm function.

The effects of 130 h of acute starvation on diaphragm contractility fatigue were studied in isolated rat diaphragm strip preparations with phrenic nerve stimulation. Compared with controls, starvation produced a reduction in body and diaphragm weights. Twitch and tetanic tensions were reduced by starvation; however, when the force was calculated as the strength (normalized for the weight or muscle cross-section area of the diaphragm), no difference was observed between the control and experimental groups. Starvation induced a significant downward shift in the force-frequency relationship, and also increased diaphragm fatigability, but it had no effect on twitch contraction and relaxation time. We conclude that 130 h of acute starvation decreases diaphragmatic force and endurance, but the strength does not change, because of the reducing diaphragmatic mass.