Changes of vasoconstriction may be measured non-invasively using pulse transit time. This study assessed the sensitivity, test-retest reliability and validity of pulse transit time during ...vasoconstriction provocation and active standing, and the predictive value of pulse transit time for blood pressure drop.
Fifty-five younger (age < 65 years) and 31 older adults (age > 70 years) underwent electrocardiography, wrist and finger photoplethysmography and continuous blood pressure and total peripheral resistance measurements during vasoconstriction provocation using a cold pressor test (21 younger adults), or active stand tests (all other participants). Pulse transit time was defined as the time lag between the electrocardiography R-peak and the peak in the photoplethysmography first derivative; sensitivity as a significant decrease relative to baseline; test-retest reliability as the intra class correlation between different repeats of the same test; validity as the association between peripheral resistance and pulse transit time; predictive value as the association between supine resting pulse transit time and mean arterial pressure drop during active standing.
Finger pulse transit time was sensitive and reliable (ICC 0.2–0.8) during vasoconstriction provocation, but wrist pulse transit time was poorly reliable (ICC 0–0.5); only finger pulse transit time was sensitive to and reliable (ICC 0.4–0.8) during active standing in both younger and older adults. Finger pulse transit time was not associated with total peripheral resistance. Supine resting pulse transit time had predictive value for blood pressure drop during active standing in older adults (β −0.16; p 0.025).
Pulse transit time was sensitive to and reliable during vasoconstriction provocation and active standing, but did not significantly differ between younger and older adults. Pulse transit time could not be demonstrated to particularly reflect vasoconstriction, but it had predictive value for blood pressure drop during active standing.
•Pulse transit time (PTT) was sensitive to an active stand test.•PTT was sensitive to vasoconstriction provocation using a cold pressor test.•PTT responses to these tests did not significantly differ between age groups.•PTT was not associated with total peripheral resistance.•PTT had predictive value for blood pressure drop during active standing.
Small nerve fibers regulate local skin blood flow in response to local thermal perturbations. Small nerve fiber function is difficult to assess with classical neurophysiological tests. In this study, ...a vasomotor response model in combination with a heating protocol was developed to quantitatively characterize the control mechanism of small nerve fibers in regulating skin blood flow in response to local thermal perturbation.
The skin of healthy subjects' hand dorsum (n=8) was heated to 42°C with an infrared lamp, and then naturally cooled down. The distance between the lamp and the hand was set to three different levels in order to change the irradiation intensity on the skin and implement three different skin temperature rise rates (0.03°C/s, 0.02°C/s and 0.01°C/s). A laser Doppler imager (LDI) and a thermographic video camera recorded the temporal profile of the skin blood flow and the skin temperature, respectively.
The relationship between the skin blood flow and the skin temperature was characterized by a vasomotor response model. The model fitted the skin blood flow response well with a variance accounted for (VAF) between 78% and 99%. The model parameters suggested a similar mechanism for the skin blood flow regulation with the thermal perturbations at 0.03°C/s and 0.02°C/s. But there was an accelerated skin vasoconstriction after a slow heating (0.01°C/s) (p-value<0.05). An attenuation of the skin vasodilation was also observed in four out of the seven subjects during the slow heating (0.01°C/s). Our method provides a promising way to quantitatively assess the function of small nerve fibers non-invasively and non-contact.
•Hand skin was heated under infrared radiation at different heating rates.•Skin blood flow responses regulated by small nerve fibers were observed.•A model was developed to characterize the skin blood flow responses.•The modelling results suggested a different response in a slow heating.•Our methods provide a non-invasive way to quantify small nerve fiber function.
Complex regional pain syndrome (CRPS) is characterized by continuous pain, disproportional to the initial trauma. It usually spreads to the distal parts of the affected limb. Besides continuing pain, ...a mix of sensory, sudo‐ and vasomotor disturbances, motor dysfunction, and trophic changes is responsible for physical complaints. Vasomotor disturbance is characterized by changes in skin temperature and color. In CRPS patients with a cold extremity, a decrease in blood flow can cause decreased tissue saturation and tissue acidosis, resulting in ischemic pain. The pathophysiology of vasomotor disturbances is not completely understood. Temperature asymmetry is generally assumed as a result of disturbance in the sympathetic nervous system. Vasodilating drugs and sympathetic blockade have been cornerstones of therapy in cold CRPS for years. However, only a limited part of these patients improve on this kind of therapies. Research has shown a pivotal role for inflammation in the pathophysiology of CRPS. Inflammation can result in endothelial dysfunction. Endothelial function plays an important role in the local regulation of vascular tone. Endothelial dysfunction could be another mechanism responsible for the vasomotor disturbances in cold CRPS. An important goal in the treatment of cold‐type CRPS is the restoration of a normal blood flow. Consequently it is important to distinguish the underlying pathophysiological mechanisms of vasomotor disturbances. A disturbance of the sympathetic nervous system may require another type of treatment than inflammation‐induced endothelial dysfunction. Diagnostic tools to distinguish these underlying pathophysiological mechanisms of vasomotor disturbances would enable a mechanism‐based treatment and improve clinical outcome.
Small nerve fiber dysfunction is an early feature of diabetic neuropathy. There is a strong clinical need for a non-invasive method to assess small nerve fiber function. Small nerve fibers mediate ...axon reflex-related vasodilation and play an important role in thermoregulation. Assessing the reflex vasodilation after local heating might elucidate some aspects of small fiber functioning. In this study, we determined the reproducibility of the reflex vasodilation after short local heating in healthy subjects, assessed with thermal imaging and laser Doppler imaging.
Healthy subjects underwent six heating rounds in one session (protocol I, N=10) or spread over two visits (protocol II, N=20). Reflex vasodilation was elicited by heating the skin to 42°C with an infrared lamp. Skin temperature and skin blood flow were recorded during heating and recovery with a thermal imaging camera and a laser Doppler imager. Skin temperature curves were fitted with a mathematical model to describe the heating and recovery phase with time constant tau (tauHeat and tauCool1).
The reproducibility of tau within a session was moderate to excellent (intra-class correlation coefficient 0.42–0.86) and good (0.71–0.72) between different sessions. Within one session the differences in tauHeat were small (bias±SD −1.3±18.9s); the bias between two visits was −1.2±12.2s. For tauCool1 the differences were also small, 1.4±6.6s within a session and between visits −1.4±11.6s.
The heat induced axon reflex-related vasodilation, assessed with thermal imaging and laser Doppler imaging, was reproducible both within a session and between different sessions. Tau describes the temporal profile in one parameter and represents the effects of all changes including blood flow and as such, is an indicator of the vasodilator function. TauHeat and tauCool1 can accurately describe the dynamics of the axon reflex-related vasodilator response in the heating and recovery phase respectively.
•Thermal imaging can measure axon reflex-related vasodilation.•Axon reflex-related vasodilation measured with thermal imaging is reproducible.•The skin temperature curve can be modeled with tau.•Tau accurately describes the skin temperature curve during heating and recovery.
Photoplethysmography (PPG) is a widely available non-invasive optical technique to visualize pressure pulse waves (PWs). Pulse transit time (PTT) is a physiological parameter that is often derived ...from calculations on ECG and PPG signals and is based on tightly defined characteristics of the PW shape. PPG signals are sensitive to artefacts. Coughing or movement of the subject can affect PW shapes that much that the PWs become unsuitable for further analysis. The aim of this study was to develop an algorithm that automatically and objectively eliminates unsuitable PWs. In order to develop a proper algorithm for eliminating unsuitable PWs, a literature study was conducted. Next, a ‘7Step PW-Filter’ algorithm was developed that applies seven criteria to determine whether a PW matches the characteristics required to allow PTT calculation. To validate whether the ‘7Step PW-Filter’ eliminates only and all unsuitable PWs, its elimination results were compared to the outcome of manual elimination of unsuitable PWs. The ‘7Step PW-Filter’ had a sensitivity of 96.3% and a specificity of 99.3%. The overall accuracy of the ‘7Step PW-Filter’ for detection of unsuitable PWs was 99.3%. Compared to manual elimination, using the ‘7Step PW-Filter’ reduces PW elimination times from hours to minutes and helps to increase the validity, reliability and reproducibility of PTT data.
A simpler method of treatment in left-sided displacement of the bovine abomasum is described. In the animal which is placed in dorsal recumbency, the abomasum is fixed to the wall of the abomasum by ...two large sutures which are perpendicular to one another. The sutures are passed through the lumen of the abomasum.
This double-blind, randomized, controlled trial investigated the effect of the phosphodiesterase-5 inhibitor tadalafil on the microcirculation in patients with cold Complex Regional Pain Syndrome ...(CRPS) in one lower extremity.
Twenty-four patients received 20 mg tadalafil or placebo daily for 12 weeks. The patients also participated in a physical therapy program. The primary outcome measure was temperature difference between the CRPS side and the contralateral side, determined by measuring the skin temperature with videothermography. Secondary outcomes were: pain measured on a Visual Analogue Scale, muscle force measured with a MicroFet 2 dynamometer, and level of activity measured with an Activity Monitor (AM) and walking tests.
At the end of the study period, the temperature asymmetry was not significantly reduced in the tadalafil group compared with the placebo group, but there was a significant and clinically relevant reduction of pain in the tadalafil group. Muscle force improved in both treatment groups and the AM revealed small, non-significant improvements in time spent standing, walking, and the number of short walking periods.
Tadalafil may be a promising new treatment for patients that have chronic cold CRPS due to endothelial dysfunction, and deserves further investigation.
The registration number in the Dutch Trial Register is ISRCTN60226869.
Background
It can take up to 30 min to determine whether or not axillary block has been successful. Pulse transit time (PTT) is the time between the R‐wave on electrocardiography (ECG) and the ...arrival of the resulting pressure pulse wave in the fingertip measured with photoplethysmography. It provides information about arterial resistance. Axillary block affects vasomotor tone causing loss of sympathetic vasoconstriction resulting in an increased PTT. Early objective assessment of a block can improve efficacy of operating room time and minimize patient's fear of possible conversion to general anesthesia. This study explores whether PTT can objectively, reliably and quickly predict a successful axillary block.
Methods
Forty patients undergoing hand surgery under axillary block were included. A three‐lead ECG and photoplethysmographic sensors were placed on both index fingers. Measurements were made from 2 min before until 30 min after induction of the block or less if the patient was transferred for operation. Afterwards, PTT was calculated as the time between the R‐wave on ECG and a reference point on the photoplethysmogram. To assess the change in PTT caused by the block, the PTT difference between the control and blocked arm was calculated. Sensitivity and specificity of PTT difference were calculated using receiver operating characteristic analysis.
Results
In a successful block, the mean PTT difference significantly increased after 3 min by 12 (standard error of the mean 3.9) ms, sensitivity 87% and specificity 71% (area under the curve 0.87, P = 0.004).
Conclusions
PTT is a reliable, quick and objective method to assess whether axillary block is going to be successful or not.
Purpose Posttraumatic cold intolerance (CI) is a frequent and important sequel after peripheral nerve injury. In this study, it is hypothesized that altered rewarming patterns after peripheral nerve ...injury are related to the degree of posttraumatic CI. This hypothesis is tested by quantitatively comparing rewarming patterns of the digits in controls and in median or ulnar nerve injury patients and by investigating relationships between rewarming patterns, sensory recovery, and CI. Methods Twelve median or ulnar nerve injury patients with a follow-up of 4 to 76 months after nerve repair and 13 control subjects had isolated cold stress testing of the hands. Video thermography was used to analyze and compare rewarming patterns of the injured and uninjured digits after cold stress testing. Temperature curves were analyzed by calculating the Q value as an indicator of heat transfer (temperature added during the first 10 minutes after start of active rewarming) and the maximum slope. Results Test–retest reliability was 0.64 and 0.79, respectively, for the Q value and maximum slope. High Q values and maximum slopes were interpreted as the presence of active rewarming. Patients with return of active rewarming had better sensory recovery and lower Blond McIndoe Cold Intolerance Severity Scale (CISS) scores. Better sensory recovery was correlated with lower CISS scores. Conclusions Test–retest reliability of cold stress testing was good, and we found a difference in rewarming patterns between nerve injury patients and controls. The presence of active rewarming in the nerve injury patients was related to sensory recovery and fewer complaints of posttraumatic CI.
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