Haemodynamic response to TENS applied to upper thoracic nerve roots in normal subjects

This study investigated the haemodynamic response to the 90-minute application of 85 Hz transcutaneous electrical nerve stimulation (TENS) to the T1 and T5 nerve roots. Comparison was made between 20 healthy subjects who had TENS stimulation and a separate group of 20 healthy subjects who rested for 90 minutes. Pulse and blood pressure were measured just prior to the start of TENS stimulation, after 30 minutes of stimulation, and after 90 minutes of stimulation (immediately after stopping TENS) or at completion of the rest time depending on group allocation. The rate pressure product was calculated from the pulse and systolic blood pressure data. Multivariate repeated measures analysis showed a significant group effect for TENS (p = 0.048). Univariate repeated measures analyses showed a significant group by time effect due to TENS on systolic blood pressure over the 90-minute time period (p = 0.028). Separate group repeated measures ANOVA showed a significant decline in heart rate (p = 0.000), systolic blood pressure (p = 0.013) and rate pressure product (p = 0.000) for the TENS group, while the control resting group showed a significant decline in heart rate only (p = 0.04). The application of 85 Hz TENS to the upper thoracic nerve roots causes no adverse haemodynamic effects in healthy subjects.

Feeding strategies for grain-fed cattle in a hot environment

Six Bos taurus (Hereford) steers (body weight 324 22 kg) were used in a 45-day study with a replicated 3 x 3 Latin-square design. Three treatments [ad libitum feeding (ADLIB); limit feeding, 85% of ad libitum (LIMIT); bunk management feeding where steers were only given access to feed from 1600 to 0800 hours the following day (BUNK)] were imposed over 3 periods, with 2 steers assigned to each treatment in each period. Cattle were managed in a temperature-controlled metabolism unit and were exposed to both thermoneutral (17.7degreesC-26.1degreesC) and hot (16.7degreesC-32.9degreesC) environmental conditions. By design, during the thermoneutral period, the ADLIB cattle displayed greater intake (P < 0.05) than the LIMIT group, with the BUNK group being intermediate. However, during the hot period, both the LIMIT and BUNK treatment groups increased feed intake 4-5%, whereas feed intake of the ADLIB treatment group declined nearly 2%. During both periods respiration rate (RR, breath/min) followed the same pattern that was observed for feed intake, with the greatest (P < 0.05) RR found in the ADLIB treatment group (81.09 and 109.55, thermoneutral and hot, respectively) and lowest (P < 0.05) RR in the LIMIT treatment group (74.47 and 102.76, thermoneutral and hot, respectively). Rectal temperature (RT) did not differ among treatments during the thermoneutral period or the first hot day, although during the thermoneutral period the ADLIB treatment group did tend to display a lower RT, possibly as a result of other physiological processes (pulse rate and RR) aiding to keep RT lower. During the hot period, differences in RT were found on Day 5, with the LIMIT cattle having lower (P < 0.10) RT (38.92degreesC) than the ADLIB (39.18degreesC) cattle, with BUNK cattle RT (39.14degreesC) being intermediate. However, when hourly data were examined, the ADLIB cattle had greater(P < 0.05) RT than the BUNK and LIMIT at 1800 hours and greater RT (P < 0.05) than the LIMIT group at 1400, 1500, and 1600 hours. Clearly, a change in diurnal RT pattern was obtained by using the LIMIT and BUNK feeding regimen. Both of these groups displayed a peak RT during the hot conditions, between 2100 and 2200 hours, whereas the ADLIB group displayed a peak RT between 1400 and 1500 hours, a time very close to when peak climatic stress occurs. Based on these results it is apparent that feedlot managers could alleviate the effects of adverse hot weather on cattle by utilising either a limit-feeding regimen or altering bunk management practices to prevent feed from being consumed several hours prior to the hottest portion of the day.

Hormonal growth-promotant effects on grain-fed cattle maintained under different environments

Six steers (3/4 Charolaisx1/4 Brahman) (mean body weight 314 +/- 27 kg) and six spayed heifers (3/5 Shorthornx2/5 Red Angus) (mean body weight 478 +/- 30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; degrees C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9 +/- 0.9 degrees C ambient temperature (T-A) and 61.7 +/- 22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2 +/- 4 degrees C (T-A) and 78.3 +/- 13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6 +/- 0.9 degrees C (T-A) and 63.4 +/- 1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P < 0.05) on cold days and greater (P < 0.05) on hot days compared to TNL. On hot days, RTs, were 0.62 degrees C higher after compared to before implanting. Across all conditions, RTs were > 0.5 degrees C greater (P < 0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were > 0.8 degrees C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2-0.35 degrees C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P < 0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P < 0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.

Variability in heart rate estimates from different pulse oximeters

Since its introduction, pulse oximetry has become a conventional clinical measure. Besides being arterial blood oxygen saturation (SpO2) measure, pulse oximeters can be used for other cardiovascular measurements, like heart rate (HR) estimations, derived from its photo plethysmographic (PPG) signals. The temporal coherence of the PPG signals and thereby HR estimates are heavily dependent on its minimal phase variability. A Masimo SET Rad-9TM, Novametrix Oxypleth and a custom designed PPG system were investigated for their relative phase variation. R-R intervals from electro-cardiogram (ECG) were recorded concurrently as reference. PPG signals obtained from the 3 systems were evaluated by comparing their respective beat-to-beat (B-B) intervals with the corresponding R-R estimates during a static test. For their relative B-B comparison to the ECG, Novametrix system differed 0.680.52% (p

Relationships between blood pressure and heart rate in the saltwater crocodile Crocodylus porosus

The cardiac limb of the baroreflex loop was studied in the saltwater crocodile Crocodylus porosus, The classical pharmacological methodology using phenylephrine and sodium nitroprusside was used to trigger blood pressure changes, and the resulting alterations in heart rate were analysed quantitatively using a logistic function. Interindividual differences in resting heart rates and blood pressures were observed, but all seven animals displayed clear baroreflex responses. Atropine and sotalol greatly attenuated the response. A maximal baroreflex gain of 7.2 beats min(-1) kPa(-1) was found at a mean aortic pressure of 6.1 kPa, indicating the active role of the baroreflex in a wide pressure range encompassing hypotensive and hypertensive states. At the lowest mean aortic pressures (5.0 kPa), the synergistic role of the pulmonary-to-systemic shunt in buffering the blood pressure drop also contributes to blood pressure regulation, Pulse pressure showed a better correlation,vith heart rate and also a higher gain than mean aortic, systolic or diastolic pressures, and this is taken as an indicator of the existence of a differential control element working simultaneously with a linear proportional element.

Physiologic parameters that affect pulse transit time difference between the upper and lower limbs in children

Pulse wave velocity (PWV) is a known parameter that is related to arterial distensibility. However, its potential is hampered by the absence of appropriate techniques to estimate it noninvasively. PWV can be used as an assessment of increased arterial stiffness that is linked to systolic hypertension, excess cardiovascular morbidity and mortality.(1,2)

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O-2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400-600 mumol photons m(-2) s(-1). O-2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm'-Ft)/Fm') decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0-300 mumol photons m(-2) s(-1)), there was a significant correlation between O-2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O-2 evolution tended towards an asymptote. However at high irradiance levels (600-1200 mumol photons m-(2) s(-1)) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3-], [NH4+] and [HPO42-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O-2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O-2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.

Update on intrapartum fetal pulse oximetry

This article examines the current status of fetal pulse oximetry (FPO) as a means of intrapartum assessment of fetal wellbeing. FPO has been developed to a stage where it is a safe and accurate indicator of intrapartum fetal oxygenation. In general, sliding the FPO sensor along the examiner's fingers and through the cervix, to lie alongside the fetal cheek or temple is easy The recent publication of a randomised controlled trial (RCT) of FPO versus conventional intrapartum monitoring has validated its use to reduce caesarean section rates for nonreassuring fetal status. An Australian multicentre RCT is currently underway. Maternal satisfaction rates with FPO are high. FPO may be used during labour when the electronic fetal heart rate trace is nonreassuring or when conventional monitoring is unreliable, such as with fetal arrhythmias. If the fetal oxygen saturation (FSpO(2)) values are < 30%, prompt obstetric intervention is indicated, such as fetal scalp blood sampling or delivery FSpO(2) monitoring should not form the sole basis of intrapartum fetal welfare assessment. Rather, the whole clinical picture should be considered.

Variability in time delay between two models of pulse oximeters for deriving the photoplethysmographic signals

Pulse oximetry is commonly used as an arterial blood oxygen saturation (SaO(2)) measure. However, its other serial output, the photoplethysmography (PPG) signal, is not as well studied. Raw PPG signals can be used to estimate cardiovascular measures like pulse transit time (PTT) and possibly heart rate (HR). These timing-related measurements are heavily dependent on the minimal variability in phase delay of the PPG signals. Masimo SET (R) Rad-9 (TM) and Novametrix Oxypleth oximeters were investigated for their PPG phase characteristics on nine healthy adults. To facilitate comparison, PPG signals were acquired from fingers on the same hand in a random fashion. Results showed that mean PTT variations acquired from the Masimo oximeter (37.89 ms) were much greater than the Novametrix (5.66 ms). Documented evidence suggests that I ms variation in PTT is equivalent to I mmHg change in blood pressure. Moreover, the PTT trend derived from the Masimo oximeter can be mistaken as obstructive sleep apnoeas based on the known criteria. HR comparison was evaluated against estimates attained from an electrocardiogram (ECG). Novametrix differed from ECG by 0.71 +/- 0.58% (p < 0.05) while Masimo differed by 4.51 +/- 3.66% (p > 0.05). Modem oximeters can be attractive for their improved SaO(2) measurement. However, using raw PPG signals obtained directly from these oximeters for timing-related measurements warrants further investigations.

Predictive regression equations and clinical uses of peripheral pulse timing characteristics in children

Studies have shown that increased arterial stiffening can be an indication of cardiovascular diseases like hypertension. In clinical practice, this can be detected by measuring the blood pressure (BP) using a sphygmomanometer but it cannot be used for prolonged monitoring. It has been established that pulse wave velocity (PWV) is a direct measure of arterial stiffening but its usefulness is hampered by the absence of non-invasive techniques to estimate it. Pulse transit time (PTT) is a simple and non-invasive method derived from PWV. However, limited knowledge of PTT in children is found in the present literature. The aims of this study are to identify independent variables that confound PTT measure and describe PTT regression equations for healthy children. Therefore, PTT reference values are formulated for future pathological studies. Fifty-five Caucasian children (39 male) aged 8.4 +/- 2.3 yr (range 5-12 yr) were recruited. Predictive equations for PTT were obtained by multiple regressions with age, vascular path length, BP indexes and heart rate. These derived equations were compared in their PWV equivalent against two previously reported equations and significant agreement was obtained (p < 0.05). Findings herein also suggested that PTT can be useful as a continuous surrogate BP monitor in children.

Age-related factors that confound peripheral pulse timing characteristics in Caucasian children

Characteristics obtained from peripheral pulses can be used to assess the status of cardiovascular system of subjects. However, nonintrusive techniques are preferred when prolonged monitoring is required for their comfort. Pulse transit time ( PTT) measurement has showed its potentials to monitor timing changes in peripheral pulse in cardiovascular and respiratory studies. In children, the common peripheries used for these studies are fingers or toes. Presently, there is no known study conducted on children to investigate the possible physiologic parameters that can confound PTT measure at these sites. In this study, PTT values from both peripheral sites were recorded from 55 healthy Caucasian children ( 39 male) with mean age of 8.4 +/- 2.3 years ( range 5 - 12 years). Peripheries' path length, heart rate, systolic blood pressure, diastolic blood pressure ( DBP) and mean arterial pressure ( MAP) were measured to investigate their contributions to PTT measurement. The results reveal that PTT is significantly related to all parameters ( P< 0.05), except for DBP and MAP. Age is observed to be the dominant factor that affects PTT at both peripheries in a child. Regression equations for PTT were derived for measuring from a finger and toe, ( 6.09 age + 189.2) ms and ( 6.70 age + 243.0) ms, respectively.

Pulse transit time changes observed with different limb positions

Pulse transit time (PTT) is a non-invasive measure of arterial compliance. It can be used to assess instantaneous blood pressure (BP) changes in continual cardiovascular measurement such as during overnight respiratory sleep studies. In these studies, periodic changes in limb position can occur randomly. However, little is known about their possible effects on PTT monitored on the various limbs. The objective of this study was to evaluate PTT differences on all four limbs during two positional changes (lowering and raising of a limb). Ten healthy adults (seven male) with a mean age of 27.0 years were recruited in this study. The results showed that the limb that underwent a positional change had significant (p < 0.05) local PTT differences when compared to its nominal baseline value, whereas PTT changes in the other remaining limbs were insignificant (p > 0.05). The mean PTT value measured from a vertically-raised limb increased by 42.7 ms, while it decreased by 28.1 ms with a half-lowered limb. The PTT differences observed during positional change can be contributed to by the complex interactions between hydrostatic pressure changes, autonomic and local autoregulation experienced in these limbs. Hence the findings herein suggest that PTT is able to reflect local circulatory responses despite changes in the position of other limbs. This can be useful in prolonged clinical observations where limb movements are expected.

Intrapartum fetal scalp lactate sampling for fetal assessment in the presence of a non-reassuring fetal heart rate trace (Protocol)

This is the protocol for a review and there is no abstract. The objectives are as follows: To evaluate the effectiveness and risks of fetal scalp lactate sampling in the assessment of fetal wellbeing during labour, compared with no testing or alternative additional testing (pH, fetal pulse oximetry, etc) for women exhibiting a non-reassuring cardiotocograph trace. A secondary objective of the review is to determine whether effectiveness and risks of intrapartum fetal scalp lactate sampling is influenced by the following: stage of labour; gestation less than 37 completed weeks, greater than or equal to 37 completed weeks; additional tests performed to confirm the presence or absence of fetal acidemia during labour.