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- A'roch, Roman, 1959-
(författare)
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Left ventricular function's relation to load, experimental studies in a porcine model
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Loading conditions are recognized to influence ventricular function according to the Starling relationship for length/stretch and force. Many modern echocardiographic parameters which have been announced as describing ventricular function and contractile status, may be confounded by uncontrolled and unmeasured load. These studies aimed to measure the relation between four different types of assessments of ventricular dysfunction and degrees of load. Study examined the ‘myocardial performance index’ (MPI). Study II examined long axis segmental mechanical dyssynchrony. Study III examined tissue velocities, and Study IV examined ventricular twist. All studies aimed to describe the relation of these parameters both to load and to inotropic changes. Methods: In anesthetized juvenile pigs, left ventricular (LV) pressure and volume were measured continuously and their relationship (LVPVR) was analysed. Preload alterations were brought about by inflation of a balloon tipped catheter in the inferior vena cava (IVCBO). Inotropic interventions were brought about by either an overdose of anesthetic (combine intravenous pentobarbital and inhaled isoflurane, Study I), or beta blocker and calcium channel blocker given in combination (Studies III and IV). In one study (II), global myocardial injury and dysfunction was induced by endotoxin infusion. MPI measurements were derived from LVPVR heart cycle intervals for isovolumic contraction and relaxation as well as ejection time. Long axis segmental dyssynchrony was derived by analyzing for internal flow and time with segmental dyssynchronous segment volume change during systole, hourly before and during 3 hours of endotoxin infusion. Myocardial tissue velocities were measured during IVCBO at control, during positive and then later negative inotropic interventions. The same for apical and base circumferential rotational velocities by speckle tracking. Load markers (including end-diastolic volume) were identified for each beat, and the test parameters were analysed together with load for a relation. The test parameters were also tested during single apneic beats for a relation to inotropic interventions. Results: MPI demonstrated a strong and linear relationship to both preload and after-load, and this was due to changes in ejection time, and not the isovolumic intervals. Long axis segmental dyssynchrony increased during each hour of endotoxin infusion and global myocardial injury. This dysynchrony parameter was independent of load when tested by IVCBO. Peak systolic velocities were strongly load-independent, though not in all the inotropic situations and by all measurement axes. Peak systolic strain was load-dependent, and not strongly related to inotropic conditions. Peak systolic LV twist and untwist were strongly load-dependent. Conclusions: MPI is strongly load-dependent, and can vary widely in value for the same contractile status if the load is varied. Mechanical dyssynchrony measures are load-independen in health and also in early global endotoxin myocardial injury and dysfunction. Peak sytole velocities are a clinically robust parameter of LV regional and global performance under changing load, though peak systolic strain seems to be load-dependent. Left ventricular twist and untwist are load-dependent in this pig model.
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| 2. |
- Brändström, Helge, 1953-
(författare)
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Accidental hypothermia and local cold injury : physiological and epidemiological studies on risk
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: (Papers I and II) The objectives were to first determine incidence and contributing factors to cold-related injuries in northern Sweden, both those that led to hospitalization and those that led to fatality. (Papers III and IV) A further aim was to assess post-cooling hand-rewarming responses and effects of training in a cold environment, both on fingertip rewarming and on function of the autonomic nervous system, to evaluate if there was adaptation related to prolonged occupational cold exposure.Methods: In a retrospective analysis, cases of accidental cold-related injury with hospital admission in northern Sweden during 2000-2007 were analyzed (Paper I). Cases of fatal hypothermia in the same region during 1992-2008 were analyzed (Paper II). A cohort of volunteers was studied before and after many months of occupational cold exposure. Subject hand rewarming response was measured after a cold hand immersion provocation and categorized as slow, moderate or normal in rewarming speed. This cold provocation and rewarming assessment was performed before and after their winter training. (Paper III). Heart rate variability (HRV) was analyzed from the same cold provocation/recovery sequences (Paper IV).Results: (Paper I) For the 379 cases of hospitalization for cold-related injury, annual incidences for hypothermia, frostbite, and drowning were 3.4/100,000, 1.5/100,000, and 1.0/100,000 inhabitants, respectively. Male gender was more frequent for all categories. Annual frequencies for hypothermia hospitalizations increased during the study period. Hypothermia degree and distribution of cases were 20 % mild (between 32 and 35ºC), 40% moderate (31.9 to 28ºC), and 24% severe (< 28ºC), while 12% had temperatures over 35.0ºC. (Paper II) The 207 cases of fatal hypothermia showed an annual incidence of 1.35 per 100,000 inhabitants, 72% in rural areas, 93% outdoors, 40% found within 100 meters of a building. Paradoxical undressing was documented in 30%. Ethanol was detected in femoral vein blood in 43%. Contributing co-morbidity was common including heart disease, previous stroke, dementia, psychiatric disease, alcoholism, and recent trauma. (Paper III) Post-training, baseline fingertip temperatures and cold recovery variables in terms of final rewarming fingertip temperature and vasodilation time increased significantly in moderate and slow rewarmers. Cold-related injury (frostbite) during winter training occured disproportionately more often in slow rewarmers (4 of the 5 injuries). (Paper IV) At ‘pre- winter-training’, normal rewarmers had higher power for low frequency and high frequency heart rate variability. After cold acclimatization (post-training), normal rewarmers showed lower resting power values for the low frequency and high frequency heart rate variability components. Conclusions: Hypothermia and cold injury continues to cause injury and hospitalization in the northern region of Sweden. Assessment and management is not standardized across hospitals. With the identification of groups at high risk for fatal hypothermia, it should be possible to reduce the incidence, particularly for highest risk subjects; rural, living alone, alcohol-imbibing, and psychiatric diagnosis-carrying citizens. Long-term cold-weather training may affect hand rewarming patters after a cold provocation, and a warmer baseline hand temperature with faster rewarming after a cold provocation may be associated with less general risk for frostbite. Heart rate variability results support the conclusion that cold adaptation in the autonomic nervous system occurred in both groups, though the biological significance of this is not yet clear.
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