Clinical Physiology and Functional Imaging
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Effects of cellular phone use on ear canal temperature measured by NTC thermistors Summary The earlier studies using phantom models and human subjects concerning warming effects during cellular phone use have been controversial, partly because radiofrequency (RF) exposures have been variable. In this randomized, double‐blind, placebo‐controlled crossover trial, 30 healthy subjects were submitted to 900 MHz (2W) and 1800 MHz (1W) cellular phone RF exposure, and to sham exposure in separate study sessions. Temperature signals were recorded continuously in both ear canals before, during and after the 35‐min RF exposure and the 35‐min sham exposure sessions. Temperature was measured by using small‐sized NTC thermistors placed in the ear canals through disposable ear plugs. The mean temperature changes were determined during a set cardiovascular autonomic function studies: during a 5‐min controlled breathing test, during a 5‐min spontaneous breathing test, during 7‐min head‐up tilting, 1‐min before, during and after two consecutive Valsalva manoeuvres and during a deep breathing test. Temperatures in the exposed ear were significantly higher during RF exposures compared with sham exposure in both 900 and 1800 MHz studies with maximum differences of 1·2 ± 0·5°C (900 MHz exposure) and 1·3 ± 0·7°C (1800 MHz exposure). Temperatures in the RF‐exposed ear were also significantly higher during the postexposure period compared with post‐sham exposure period with maximum differences of 0·6 ± 0·3°C for 900 MHz and 0·5 ± 0·5°C for 1800 MHz. The results of this study suggest that RF exposure to a cellular phone, either using 900 or 1800 MHz with their maximal allowed antenna powers, increases the temperature in the ear canal. The reason for the ear canal temperature rising is a consequence of mobile phone battery warming during maximal antenna power use. The earlier published articles do not indicate that temperature rising in the ear canal has any significant contribution from the RF fields emitted from mobile phones.
Clinical Physiology and Functional Imaging - Tập 27 Số 3 - Trang 162-172 - 2007
Determination of left ventricular long‐axis orientation using MRI: changes during the respiratory and cardiac cycles in normal and diseased subjects Summary Background: It has previously been shown that magnetic resonance imaging (MRI) can be used to accurately determine left ventricular (LV) long‐axis orientation in healthy individuals. However, the inter‐ and intra‐observer variability in patients with acute coronary syndrome (ACS) and chronic heart failure (CHF) has not been explored. Furthermore, the changes in LV long‐axis orientation because of respiration and during the cardiac cycle remain to be determined.Methods: LV long‐axis orientation was determined by MRI in the frontal and transverse planes in 44 subjects with no cardiac disease, 20 ACS patients and 13 CHF patients. Changes in LV long‐axis orientation because of respiration were assessed in a subset of 25 subjects. Changes during the cardiac cycle were assessed in six subjects from each subject group. Reproducibility was assessed by a re‐examination of 17 subjects after 28 days.Results: The inter‐ and intra‐observer variability for LV long‐axis orientation was low for all subject groups. The difference between the baseline and the 28 days examinations was −1·4 ± 5·9° and −0·8 ± 4·4° in the frontal and transverse planes, respectively. No significant change in LV long‐axis orientation was found between end‐expiration and end‐inspiration (frontal plane, P = 0·63 and transverse plane, P = 0·42; n = 25). No significant difference in change of the LV long‐axis orientation during the cardiac cycle was found between the subject groups (frontal plane, chi‐square 1·8, P = 0·40 and transverse plane, chi‐square 5·7, P = 0·06).Conclusions: There is a low inter‐and intra‐observer variability and a high reproducibility for determining LV long‐axis orientation in patients with no cardiac disease as well as in patients with ACS or CHF. There is no significant change in LV long‐axis orientation due to respiration, and only small changes during the cardiac cycle in these groups.
Clinical Physiology and Functional Imaging - Tập 25 Số 5 - Trang 286-292 - 2005
Central fatigue of the first dorsal interosseous muscle during low‐force and high‐force sustained submaximal contractions Summary The aim of this study was to compare the extent of central fatigue in the first dorsal interosseous (FDI) muscle of healthy adults in low, moderate and high‐force submaximal contractions. Nine healthy adults completed four experimental sessions where index finger abduction force was recorded during voluntary contractions and in response to brief trains (five pulses at 100 Hz) of electrical stimulation. The ability to maximally activate FDI under volition, or voluntary activation, and its change with sustained activity (central fatigue) was assessed using the twitch interpolation technique. The fatigue tasks consisted of continuous isometric index finger abduction contractions held until exhaustion at four target force levels: 30%, 45%, 60% and 75% of the maximal voluntary contraction. The main finding was the presence of central fatigue for the 30% task, but not for the three other fatigue tasks. The extent of central fatigue was also associated with changes in a measure reflecting the status of peripheral structures/mechanisms. It appears that central fatigue contributed to task failure for the lowest force fatigue task (30%), but not for the other (higher) contraction intensities.
Clinical Physiology and Functional Imaging - Tập 27 Số 5 - Trang 298-304 - 2007
Predicted maximal heart rate for upper body exercise testing Summary Age‐predicted maximal heart rate (HR MAX ) equations are commonly used for the purpose of prescribing exercise regimens, as criteria for achieving maximal exertion and for diagnostic exercise testing. Despite the growing popularity of upper body exercise in both healthy and clinical settings, no recommendations are available for exercise modes using the smaller upper body muscle mass. The purpose of this study was to determine how well commonly used age‐adjusted prediction equations for HR MAX estimate actual HR MAX for upper body exercise in healthy young and older adults. A total of 30 young (age: 20 ± 2 years, height: 171·9 ± 32·8 cm, mass: 77·7 ± 12·6 kg) and 20 elderly adults (age: 66 ± 6 years, height: 162 ± 8·1 cm, mass: 65·3 ± 12·3 kg) undertook maximal incremental exercise tests on a conventional arm crank ergometer. Age‐adjusted maximal heart rate was calculated using prediction equations based on leg exercise and compared with measured HR MAX data for the arms. Maximal HR for arm exercise was significantly overpredicted compared with age‐adjusted prediction equations in both young and older adults. Subtracting 10–20 beats min−1 from conventional prediction equations provides a reasonable estimate of HR MAX for upper body exercise in healthy older and younger adults.
Clinical Physiology and Functional Imaging - Tập 36 Số 2 - Trang 155-158 - 2016
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