Breathing Protocol Research Articles

Efficient and cost‐effective estimation of the influence of respiratory variables on respiratory sinus arrhythmia

Researchers are interested in respiratory sinus arrhythmia (RSA) as an index of cardiac vagal activity. Yet, debate exists about how to account for respiratory influences on quantitative indices of RSA. T. Ritz, M. Thons, and B. Dahme (2001) developed a within-individual correction procedure by which the effects of respiration on RSA may be estimated using regression models. We replicated their procedure substituting a spectral high-frequency measure of RSA for a time-domain statistic and a respiratory belt's relative measure of tidal volume for the direct assessment provided by a pneumotachograph. The standardized slopes from the respiratory belt and pneumotachography-derived regression equations (estimated across a 6-min paced breathing protocol) were positively correlated (r=0.93, p<.001); correlations were similar across 2- and 4-min time courses parsed from the 6-min protocol. Our results offer methodological alternatives to the research community.

Monitoring of hemodynamic changes induced in the healthy breast through inspired gas stimuli with MR-guided diffuse optical imaging

The modulation of tissue hemodynamics has important clinical value in medicine for both tumor diagnosis and therapy. As an oncological tool, increasing tissue oxygenation via modulation of inspired gas has been proposed as a method to improve cancer therapy and determine radiation sensitivity. As a radiological tool, inducing changes in tissue total hemoglobin may provide a means to detect and characterize malignant tumors by providing information about tissue vascular function. The ability to change and measure tissue hemoglobin and oxygenation concentrations in the healthy breast during administration of three different types of modulated gas stimuli (oxygen/ carbogen, air/carbogen, and air/oxygen) was investigated. Subjects breathed combinations of gases which were modulated in time. MR-guided diffuse optical tomography measured total hemoglobin and oxygen saturation in the breast every 30 s during the 16 min breathing stimulus. Metrics of maximum correlation and phase lag were calculated by cross correlating the measured hemodynamics with the stimulus. These results were compared to an air/air control to determine the hemodynamic changes compared to the baseline physiology. This study demonstrated that a gas stimulus consisting of alternating oxygen/carbogen induced the largest and most robust hemodynamic response in healthy breast parenchyma relative to the changes that occurred during the breathing of room air. This stimulus caused increases in total hemoglobin and oxygen saturation during the carbogen phase of gas inhalation, and decreases during the oxygen phase. These findings are consistent with the theory that oxygen acts as a vasoconstrictor, while carbogen acts as a vasodilator. However, difficulties in inducing a consistent change in tissue hemoglobin and oxygenation were observed because of variability in intersubject physiology, especially during the air/oxygen or air/carbogen modulated breathing protocols. MR-guided diffuse optical imaging is a unique tool that can measure tissue hemodynamics in the breast during modulated breathing. This technique may have utility in determining the therapeutic potential of pretreatment tissue oxygenation or in investigating vascular function. Future gas modulation studies in the breast should use a combination of oxygen and carbogen as the functional stimulus. Additionally, control measures of subject physiology during air breathing are critical for robust measurements.

Operational point of neural cardiovascular regulation in humans up to 6 months in space

Entering weightlessness affects central circulation in humans by enhancing venous return and cardiac output. We tested whether the operational point of neural cardiovascular regulation in space sets accordingly to adopt a level close to that found in the ground-based horizontal position. Heart rate (HR), finger blood and brachial blood pressure (BP), and respiratory frequency were collected in 11 astronauts from nine space missions. Recordings were made in supine and standing positions at least 10 days before launch and during spaceflight (days 5-19, 45-67, 77-116, 146-180). Cross-correlation analyses of HR and systolic BP were used to measure three complementary aspects of cardiac baroreflex modulation: 1) baroreflex sensitivity, 2) number of effective baroreflex estimates, and 3) baroreflex time delay. A fixed breathing protocol was performed to measure respiratory sinus arrhythmia and low-frequency power of systolic BP variability. We found that HR and mean arterial pressure did not differ from preflight supine values for up to 6 mo in space. Respiration frequency tended to decrease during prolonged spaceflight. Concerning neural markers of cardiovascular regulation, we observed in-flight adaptations toward homeostatic conditions similar to those found in the ground-based supine position. Surprisingly, this was not the case for baroreflex time delay distribution, which had somewhat longer latencies in space. Except for this finding, our results confirm that the operational point of neural cardiovascular regulation in space sets to a level close to that of an Earth-based supine position. This adaptation level suggests that circulation is chronically relaxed for at least 6 mo in space.

ＣＴ‐ｔｒａｎｓｍｉｓｓｉｏｎの呼吸管理がＰＥＴ／ＣＴの融合精度に与える影響―６００人を対象とした標準呼気と自由呼吸の比較―

Image misregistration can occur in fusion PET/CT, because of motion artifacts caused by the management of respiration. The standard imaging protocol of the CT component of PET/CT is normal expiration (NormExp) or free breathing (FB). The objective of this study was to compare NormExp and FB for the optimal breathing protocol for PET/CT scans. A total of 600 consecutive patients were examined using lutetium oxyorthosilicate (LSO)-based PET/CT. CT was acquired during NormExp (i.e., the level reached when the patient exhaled without forcing expiration and then held the breath) in 300 patients and during FB in 300 patients. The profile of liver measured along body axis was assessed. The distance of profile centers between the PET image and the CT image was measured. The misalignment between profile centers (PET) and profile centers (CT) was compared between NormExp and FB using the histogram of patients. An F test was used to test if the variances of two misalignments are equal. Next, the relationship between misalignment and age was evaluated in two managements of respiration. There was no significant difference between NormExp and FB in the histogram. However, significant misalignments (>10 cm) were found with NormExp. Patient age may have influenced the mismatch. FB is recommended for geriatric patients during acquisition of attenuation correction CT data sets.

Respiratory sinus arrhythmia on the ESA-short-arm human centrifuge

In this article, we investigated the hypothesis that the effects of hypergravity on respiratory sinus arrhythmia (RSA) can mimic the effects observed after spaceflight cardiovascular deconditioning. Artificial gravity along the head-to-feet axis on a short-arm centrifuge induces gravity gradients. This physiological condition of significantly higher g at the feet than at the heart level is specific and likely induces blood sequestration in the lower limbs. After spaceflight, astronauts are in a condition of cardiovascular deconditioning, where blood pooling in the lower part of the body and autonomic adaptation are factors contributing to orthostatic intolerance and changes in heart-rate variability (HRV). ECG and respiration were recorded during imposed and controlled breathing (ICB) protocols, which were repeated at different levels of artificial gravity as well as during supine and standing control conditions, and the changes were analyzed.

A randomized controlled trial of a controlled breathing protocol on heart rate variability following myocardial infarction or coronary artery bypass graft surgery

Objectives: To determine whether a controlled breathing programme increases heart rate variability following an acute myocardial infarction and/or coronary artery bypass graft surgery. Rationale: Heart rate variability is reduced following a myocardial infarction, and low heart rate variability is associated with a high mortality risk. By changing tidal volume and rate of breathing, individuals can alter beat-to-beat heart rate variability. It is hypothesized that heart rate increases with inspiration and decreases with exhalation, and that deep slow breathing enhances respiratory sinus arrhythmia, increasing heart rate variability. Design: Randomized controlled trial. Setting: Cardiac rehabilitation programme at a large academic medical centre in North Texas. Subjects: From 2001 to 2005, 44 patients, age 46—65 years, who had a myocardial infarction and/or undergone coronary artery bypass graft surgery 1—8 weeks previously and were referred to the Cardiac Rehabilitation Program. Intervention: Patients were randomized to either usual cardiac rehabilitation or cardiac rehabilitation with controlled breathing (6 breaths/min for 10 minutes twice daily during the eight-week treatment period). Main measures: Weekly measurements of total power and standard deviation of the mean normal to normal RR interval (SDNN), and fortnightly measurements of respiratory sinus arrhythmia were taken using Biocom Technologies Heart Rhythm Scanner and Tracker software. Results: No significant difference in change were seen between groups in SDNN (P = 0.3984), baseline respiratory sinus arrhythmia (P = 0.6556) or total power (P = 0.6184). Conclusion: Results suggest participation in the controlled breathing programme offered no additional benefit in increasing heart rate variability following myocardial infarction or coronary artery bypass graft surgery. However, 77% of study patients were on heart rate-lowering medications, which may have masked changes in heart rate variability.

FDG-PET-basierte Bestrahlungsplanung von nicht kleinzelligen Bronchialkarzinomen: Optimales Atemprotokoll und Patientenpositionierung – ein intraindividueller Vergleich

PURPOSE: FDG-PET and PET / CT is increasingly used for radiotherapy (RT) planning in non-small-cell lung carcinoma (NSCLC). The planning process is often based on separately-acquired FDG-PET / CT and planning CT. We compared intraindividual differences between PET acquired in diagnostic and radiotherapy treatment position coregistered with planning CTs acquired using different breathing protocols. METHODS AND MATERIALS: Sixteen patients with NSCLC underwent two PET acquisitions (diagnostic position-D-PET, radiotherapy position-RT-PET) and three planning-CT acquisitions (expiration-EXP, inspiration-INS, mid-breathhold-MID) on the same day. All scans were rigidly coregistered resulting in six fused datasets: D-INS, D-EXP, D-MID, RT-INS, RT-EXP and RT-MID. Fusion accuracy was assessed by three readers at eight anatomical landmarks: lung apices, aortic arch, heart, spine, sternum, carina, diaphragm and tumor using an alignment score ranging from 1 (no alignment) to 5 (exact alignment). RESULTS: RT-PET showed better alignment with any CT than D-PET (p < 0.001). With regard to breathing, RT-MID showed the best mean alignment score (3.7 ± 1.0) followed by RT-EXP (3.5 ± 0.9) and RT-INS (3.0 ± 0.8), all differences being significant (p < 0.001). Comparing the alignment scores with regard to anatomical landmarks, the largest deviations were found at diaphragm, heart and apices. Overall, there was a fair agreement (κ = 0.48; p < 0.001) among the three readers. CONCLUSIONS: Significantly better fusion of PET and planning-CT can be reached with PET acquired in RT-position. The best intraindividual fusion results are obtained with the planning-CT performed during mid-breathhold. Our data justify the acquisition of a separate planning-PET in RT-treatment position if only a diagnostic PET-scan is available.

Fully Automated Motion Correction in First-Pass Myocardial Perfusion MR Image Sequences

This paper presents a novel method for registration of cardiac perfusion magnetic resonance imaging (MRI). The presented method is capable of automatically registering perfusion data, using independent component analysis (ICA) to extract physiologically relevant features together with their time-intensity behavior. A time-varying reference image mimicking intensity changes in the data of interest is computed based on the results of that ICA. This reference image is used in a two-pass registration framework. Qualitative and quantitative validation of the method is carried out using 46 clinical quality, short-axis, perfusion MR datasets comprising 100 images each. Despite varying image quality and motion patterns in the evaluation set, validation of the method showed a reduction of the average right ventricle (LV) motion from 1.26+/-0.87 to 0.64+/-0.46 pixels. Time-intensity curves are also improved after registration with an average error reduced from 2.65+/-7.89% to 0.87+/-3.88% between registered data and manual gold standard. Comparison of clinically relevant parameters computed using registered data and the manual gold standard show a good agreement. Additional tests with a simulated free-breathing protocol showed robustness against considerable deviations from a standard breathing protocol. We conclude that this fully automatic ICA-based method shows an accuracy, a robustness and a computation speed adequate for use in a clinical environment.

FDG-PET–Based Radiotherapy Planning in Lung Cancer: Optimum Breathing Protocol and Patient Positioning—An Intraindividual Comparison

Fluoro-2-deoxy-d-glucose (FDG)-positron emission tomography (PET) and PET/computed tomography (CT) are increasingly used for radiotherapy (RT) planning in patients with non-small-cell lung carcinoma. The planning process often is based on separately acquired FDG-PET/CT and planning CT scans. We compared intraindividual differences between PET acquired in diagnostic (D-PET) and RT treatment position (RT-PET) coregistered with planning CTs acquired using different breathing protocols. Sixteen patients with non-small-cell lung carcinoma underwent two PET acquisitions (D-PET and RT-PET) and three planning CT acquisitions (expiration [EXP], inspiration [INS], and mid-breath hold [MID]) on the same day. All scans were rigidly coregistered, resulting in six fused data sets: D-INS, D-EXP, D-MID, RT-INS, RT-EXP, and RT-MID. Fusion accuracy was assessed by three readers at eight anatomic landmarks, lung apices, aortic arch, heart, spine, sternum, carina, diaphragm, and tumor, by using an alignment score ranging from 1 (no alignment) to 5 (exact alignment). The RT-PET showed better alignment with any CT than D-PET (p < 0.001). With regard to breathing, RT-MID showed the best mean alignment score (3.7 +/- 1.0), followed by RT-EXP (3.5 +/- 0.9) and RT-INS (3.0 +/- 0.8), with all differences significant (p < 0.001). Comparing alignment scores with regard to anatomic landmarks, the largest deviations were found at the diaphragm, heart, and apices. Overall, there was fair agreement (kappa = 0.48; p < 0.001) among the three readers. Significantly better fusion of PET and planning CT can be reached with PET acquired in the RT position. The best intraindividual fusion results are obtained with the planning CT performed during mid-breath hold. Our data justify the acquisition of a separate planning PET in RT treatment position if only a diagnostic PET scan is available.

Optimal breathing protocol for dynamic contrast-enhanced MRI of solitary pulmonary nodules at 3 T

The purpose of this study was to evaluate optimal breathing maneuvers that minimize lung parenchymal movement for dynamic contrast-enhanced MRI (DCE-MRI), which requires longer scan times, beyond the limit of a single breath hold. A healthy volunteer was scanned on a 3 T MR scanner using two different breathing maneuvers. In the first, the healthy volunteer was instructed to hold his breath as much as possible and breathe in between breath holds while an image was obtained. In the second, the volunteer was instructed to breathe shallowly and freely throughout the scan. On the obtained images, the excursion of the highest point of the right diaphragm and the pulmonary vessel branches located in the four different anatomic regions of the lung were measured in two orthogonal planes. A patient with a solitary pulmonary nodule (SPN) underwent DCE-MRI utilizing a 2D spoiled gradient-echo (SPGR) sequence while the patient breathed shallowly and freely during the scan. The standard deviations of the excursion of the highest point and selected pulmonary vessels were much smaller during shallow, free breathing maneuver scans than those during breath hold maneuver scans. A dynamic perfusion-fitting curve of the SPN was obtained during the DCE-MRI using shallow free breathing. Shallow, free breathing allows smaller diaphragmatic cranial caudal and lung parenchymal displacements. Therefore, it can be useful during exams where targeting of the lesion is necessary, in studies with long scan times, such as dynamic MRI. This breathing maneuver makes it possible to analyze SPN with DCE-MRI while making use of the advantages of a higher magnetic field in conjunction.

Evaluation of Image Registration in PET/CT of the Liver and Recommendations for Optimized Imaging

Multimodality PET/CT of the liver can be performed with an integrated (hybrid) PET/CT scanner or with software fusion of dedicated PET and CT. Accurate anatomic correlation and good image quality of both modalities are important prerequisites, regardless of the applied method. Registration accuracy is influenced by breathing motion differences on PET and CT, which may also have impact on (attenuation correction-related) artifacts, especially in the upper abdomen. The impact of these issues was evaluated for both hybrid PET/CT and software fusion, focused on imaging of the liver. Thirty patients underwent hybrid PET/CT, 20 with CT during expiration breath-hold (EB) and 10 with CT during free breathing (FB). Ten additional patients underwent software fusion of dedicated PET and dedicated expiration breath-hold CT (SF). The image registration accuracy was evaluated at the location of liver borders on CT and uncorrected PET images and at the location of liver lesions. Attenuation-correction artifacts were evaluated by comparison of liver borders on uncorrected and attenuation-corrected PET images. CT images were evaluated for the presence of breathing artifacts. In EB, 40% of patients had an absolute registration error of the diaphragm in the craniocaudal direction of >1 cm (range, -16 to 44 mm), and 45% of lesions were mispositioned >1 cm. In 50% of cases, attenuation-correction artifacts caused a deformation of the liver dome on PET of >1 cm. Poor compliance to breath-hold instructions caused CT artifacts in 55% of cases. In FB, 30% had registration errors of >1 cm (range, -4 to 16 mm) and PET artifacts were less extensive, but all CT images had breathing artifacts. As SF allows independent alignment of PET and CT, no registration errors or artifacts of >1 cm of the diaphragm occurred. Hybrid PET/CT of the liver may have significant registration errors and artifacts related to breathing motion. The extent of these issues depends on the selected breathing protocol and the speed of the CT scanner. No protocol or scanner can guarantee perfect image fusion. On the basis of these findings, recommendations were formulated with regard to scanner requirements, breathing protocols, and reporting.

Hybrid PET/CT of the Thorax

To determine if computer registration improves the image fusion of hybrid positron emission tomography (PET)/computed tomography (CT) data sets in the thorax acquired during different breathing maneuvers. Hybrid PET/CT scans were acquired with varying CT respiratory instructions. The scans of 64 patients with 5 different breathing maneuvers were reviewed, including expiration, suspended breath hold, quiet breathing, small breath in, and regular breath in. The PET/CT data sets were reviewed before registration, after linear registration, and combined linear/nonlinear registration. Each PET/CT data set was graded for the quality of alignment at 5 anatomical locations (diaphragm, aortic arch, heart, thoracic spine, and lung apices) and rated from 1 (very poor) to 5 (excellent). The Kruskal-Wallis test was used to compare alignment between the breathing protocols, and Wilcoxon signed rank test was used to compare the registration techniques. The quality of anatomical alignment between superimposed (nonregistered) PET and attenuation correction CT (CTAC) acquired during expiration, suspended breath hold, and quiet breathing was excellent, with no significant changes in alignment following registration. The quality of anatomical alignment between superimposed (nonregistered) PET and CTAC acquired during inspiration showed significant misalignment at the heart (P = 0.001, P < 0.0001) and diaphragm (P = 0.0001, P < 0.0001) which did not correct with linear registration. Alignment significantly improved with additional nonlinear registration at the diaphragm (P = 0.008, P = 0.0002), although cardiac misalignment remained. With hybrid PET/CT, excellent anatomical alignment between PET and CTAC scans can be achieved with CT acquisition during expiration, suspended breath hold, or quiet breathing, and additional software registration is not necessary. Nonlinear registration significantly improves alignment discrepancies at the diaphragm if inspiratory methods are used, however, cardiac misalignment remains.

Fixation devices for whole-body 18F-FDG PET/CT: Patient perspectives and technical aspects

To evaluate the use of a fixation device in whole-body postiron emission tomography/computed tomography (PET/CT). Two hundred and thirty patients were prospectively included over a period of 3 months. Different single-phase and multiphase contrast-enhanced PET/CT protocols were used for whole-body examination. An unforced expiration state was applied as breathing protocol for CT examination. Patients were placed on a deflating device (1.0 m x 1.5 m) with arms elevated but supported in order to prevent full extension in shoulders and elbows providing comfortable positioning. Image quality was assessed by means of alignment of the liver quantitatively on co-registered PET/CT images. After the examination, patients were asked to complete a survey on subjective sensations such as pain in different body regions (yes/no). They were asked to give a final evaluation for the whole-body PET/CT examination (comfortable/not comfortable). Additionally, a control group (n=30) was assessed without the aid of additional devices. Examination protocols using the device showed minor misalignment of 5 mm. Different protocols did not reveal significant differences in misalignment. When comparing the control group misalignment was significantly higher with approx. 7 mm. The majority (75%) evaluated the positioning as comfortable despite 46% of the patients in this group feeling more or less severe pain in at least one body region. For controls, misalignment was slightly higher whereas only 39% found the positioning comfortable (chi(2)=13.03; P<0.0005) and 61% reported pain (NS). Both the technical aspects and patient evaluations favour the use of the vacuum device in whole-body PET/CT examinations. In particular, in time consuming protocols using multiphase CT examination the fixation device leads to excellent co-registration quality and patient compliance.

Vergleich verschiedener Atem- und Kontrastmittelprotokolle bezüglich Bild- und Koregistrierungsqualität bei 18F-FDG-PET/CT-Untersuchungen

The purpose of this study was to establish a reliable and simple parameter for alignment evaluation and the evaluation and optimization of state-of-the-art contrast-enhanced examination protocols for (18)F FDG-PET/CT. 44 consecutive patients were referred to 4 examination protocols. Group A and B underwent single-phase, contrast-enhanced CT (90 s delay) performed either during free shallow breathing (FA; group A) or normal expiration (NormExp; group B). Groups C and D underwent arterial and portal venous multiphase examinations performed during FA (group C) or during NormExp (group D) followed by a low-dose CT scan for attenuation correction. Organ displacement in the cranio-caudal direction was correlated with a 3D-vectorial shift. For alignment evaluation discrepancies with respect to size and liver location, the spleen and kidneys were calculated. Additionally, the groups were compared with regard to the presence of CT artifacts. Cranio-caudal organ shift and 3D-vectorial shift showed a high correlation (r > 0.8). Single-phase CT scans performed during NormExp yielded better image quality (p < 0.001) and alignment (p < 0.01 for liver, spleen and right kidney) than those performed during FA. Differences in organ size did not differ during FA and NormExp. Depending on the evaluated organ, breathing and contrast protocol misalignment was in the cranio-caudal direction 0-27 mm (mean: 6.8; standard deviation: +/- 4.9) in multiphase CT compared to 0 - 11 mm (mean: 4.5 +/- 2.3) in single-phase examinations. 1. Organ shift in the cranio-caudal direction is a good and simple parameter for alignment evaluation. 2. Alignment and CT quality are best in expiration protocols. 3. Despite comparatively low alignment quality, integrated multiphase CT examinations show acceptable quality and alignment.

Optimal CT Breathing Protocol for Combined Thoracic PET/CT

The objective of this study was to determine the optimal breathing protocol for combined PET/CT scans of the thorax. Eighty combined PET/CT scans were obtained in 64 patients (30 women, 34 men; mean age, 57 years; range, 19-86 years). The 80 PET/CT scans consisted of five group of patients (16 PET/CT scans per group) who underwent whole-body combined 18F-FDG PET/CT with different CT breathing protocols: expiration, mid suspended breath-hold, quiet breathing, small breath in, and regular breath in. The quality of alignment was analyzed at the diaphragm, aortic arch, heart, thoracic spine, and lung apices using a scale of ratings from 1 (very poor) to 5 (excellent). The Kruskal-Wallis test was used to compare alignment between breathing protocols for each anatomic reference point. Alignment of the PET and CT data sets was excellent with three breathing protocols: expiration, mid suspended breath-hold, and quiet breathing, with no statistical differences. Significant misalignment occurred at the diaphragm (p < 0.0001) and heart (p < 0.0001) with the small breath-in and regular breath-in techniques. Excellent image fusion of combined PET/CT data sets in the thorax, especially at the diaphragm and heart, can be achieved with expiration, mid suspended breath-hold, or quiet breathing. Quiet breathing is recommended for optimal patient comfort during acquisition of attenuation-correction CT data sets.

Cold-Water Face Immersion Per Se Elicits Cardiac Parasympathetic Activity

Cold-water face immersion (FI) is known to produce physiological changes, including bradycardia, by stimulating the parasympathetic system. However, other factors such as sympathetic activity, intrapleural pressures, and changes in chemical mediators may also contribute to these changes. Eight healthy volunteers underwent a series of experiments designed to observe the effects of FI on heart rate and its variability, as detected using wavelet transformation. Each subject was instructed to bend over and put the entire face into an empty basin with and without breathing (protocols 1 and 2, respectively), and then perform FI in warm-water (protocols 3 and 4, respectively) and cold-water (protocols 5 and 6, respectively) while breathing and breath holding. Change in the R-R interval with FI was only significantly greater for protocol 6 than for the control procedure (protocol 1). Also, changes in the natural logarithm of high-frequency power with FI were significantly greater for protocols 5 and 6 than the protocol 1. Bradycardia associated with cold-water FI is mainly attributed to cardiac vagal activity, which is independent of both the change in body position caused by bending over a basin and breath holding.

Correlation between respiration-induced thoracic expansion and a shift of central structures

The fusion of computed tomography (CT) and positron emission tomography (PET) may improve diagnostic accuracy, but is limited by different breathing protocols. This study aimed at quantifying respiration-induced alignment errors. PET-CT was acquired in 24 patients. Contrast-enhanced whole-body CT was obtained in a single breath hold in the expiratory state of a normal breathing cycle. An inspiratory low-dose CT of the thorax was acquired in the same session, and comparison of the two CT scans was used to assess the potential mismatch of PET and CT fusion. The largest craniocaudal expansion was found in the area of the diaphragm. A considerable sagittal expansion was found in the anterior parts of the lungs. Central tracheo-bronchial structures were displaced during inspiration mainly in the anterior and caudal directions. The craniocaudal shift of central structures showed a linear correlation with the diaphragmatic expansion, whereas the sagittal shift correlated with the sagittal pleural expansion. There was, however, no correlation between craniocaudal and sagittal respiratory motion. Alignment errors are most severe in the base of the lung, but central structures are affected, too. Understanding of the main vectors of respiratory motion may help in image interpretation when PET and CT are acquired separately.

34.38 Comparison of end-expiratory breath hold and shallow breathing protocols for CT based attenuation correction of 99TC-Sestamibi myocardial perfusion images using multi-slice SPECT-CT

34.38 Comparison of end-expiratory breath hold and shallow breathing protocols for CT based attenuation correction of 99TC-Sestamibi myocardial perfusion images using multi-slice SPECT-CT

Association between short term exposure to fine particulate matter and heart rate variability in older subjects with and without heart disease

Short term increases in exposure to particulate matter (PM) air pollution are associated with increased cardiovascular morbidity and mortality. The mechanism behind this effect is unclear, although changes in autonomic control have been observed. It was hypothesised that increases in fine PM measured at the subjects' home in the preceding hour would be associated with decreased high frequency heart rate variability (HF-HRV) in individuals with pre-existing cardiac disease. Two hundred and eighty five daily 20 minute measures of HRV (including a paced breathing protocol) were made in the homes of 34 elderly individuals with (n = 21) and without (n = 13) cardiovascular disease (CVD) over a 10 day period in Seattle between February 2000 and March 2002. Fine PM was continuously measured by nephelometry at the individuals' homes. The median age of the study population was 77 years (range 57-87) and 44% were male. Models that adjusted for health status, relative humidity, temperature, mean heart rate, and medication use did not find a significant association between a 10 microg/m3 increase in 1 hour mean outdoor PM2.5 before the HRV measurement and a change in HF-HRV power in individuals with CVD (3% increase in median HF-HRV (95% CI -19 to 32)) or without CVD (5% decrease in median HF-HRV (95% CI -34 to 36)). Similarly, no association was evident using 4 hour and 24 hour mean outdoor PM2.5 exposures before the HRV measurement. No association was found between increased residence levels of fine PM and frequency domain measures of HRV in elderly individuals.

Influences of breathing patterns on respiratory sinus arrhythmia in humans during exercise

Persistence of respiratory sinus arrhythmia (RSA) has been described in humans during intense exercise and attributed to an increase in ventilation. However, the direct influence of ventilation on RSA has never been assessed. The dynamic evolution of RSA and its links to ventilation were investigated during exercise in 14 healthy men using an original modeling approach. An evolutive model was estimated from the detrended and high-pass-filtered heart period series. The instantaneous RSA frequency (FRSA, in Hz) and amplitude (ARSA, in ms) were then extracted from all recordings. A(RSA) was calculated with short-time Fourier transform. First, measurements of FRSA and ARSA were performed from data obtained during a graded and maximal exercise test. Influences of different ventilation regimens [changes in tidal volume (VT) and respiratory frequency (FR)] on ARSA were then tested during submaximal [70% peak O2 consumption (VO2peak)] rectangular exercise bouts. Under graded and maximal exercise conditions, ARSA decreased from the beginning of exercise to 61.9 +/- 3.8% VO2peak and then increased up to peak exercise. During the paced breathing protocol, normoventilation (69.4 +/- 8.8 l/min), hyperventilation (81.8 +/- 8.3 l/min), and hypoventilation (56.4 +/- 6.2 l/min) led to significantly (P < 0.01) different ARSA values (3.8 +/- 0.5, 4.6 +/- 0.8, and 2.9 +/- 0.5 ms, respectively). In addition, no statistical difference was found in ARSA when ventilation was kept constant, whatever the FR-VT combinations. Those results indicate that RSA persists for all exercise intensities and increases during the highest intensities. Its persistence and increase are strongly linked to both the frequency and degree of lung inflation, suggesting a mechanical influence of breathing on RSA.