Life continues at a metabolic level after death according to new research; which find that the heart has the most activity in the day after demise. The research, publish in Metabolomics today (Tuesday 5 March) has found that cells in parts of the body including the heart, kidney and liver; so continue to see activity at a molecular level in the 24 hours following death.
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It report in energy units per unit time ranging from watt to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria be met. These criteria include being in a physically and psychologically undisturbed state; so in a thermally neutral environment, while in the post absorptive state.
Metabolism for many mammals
In bradymetabolic animals, such as fish and reptiles; so the equivalent term standard metabolic rate (SMR) is used. It follows the same criteria as BMR, but requires the documentation of the temperature; which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data; so a practice that led to problems in defining “standard” rates of metabolism for many mammals.
Metabolism comprises the processes that the body needs to function. Basal metabolic rate is the amount of energy per unit time that a person needs to keep the body functioning at rest. Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and nerve function, and contraction of muscles. Basal metabolic rate (BMR) affects the rate that a person burns calories and ultimately whether that individual maintains, gains, or loses weight.
The basal metabolic rate accounts for about 60 to 75% of the daily calorie expenditure by individuals. It is influence by several factors. BMR typically declines by 1–2% per decade after age 20; so mostly due to loss of fat-free mass, although the variability between individuals is high. In particular, the team saw that molecular activity in the heart and kidneys continued to operate; through to produce energy molecules prior nucleic acid degradation.
Heart ‘stopping’ at point of death
In contrast, the skin saw very little activity in the same time frame. The study certainly open our eyes to how parts of the body continue to provide an environment for molecular activity in the hours after death. It was particularly interesting to note that the heart was one of the organs that saw the most activity over 24 hours after death when they traditionally think of the heart ‘stopping’ at the point of death.
The study is also a proof of concept about a new field of research to better determine time of death. The team note that all of the activity they observe was consistent for anaerobic activity over the time periods after death, and suggest that the new field of ‘thanatometabolomics’ be use to help with forensic analysis. We were amazed to find that even after a mouse is dead, most of its cells are active and still fighting to compensate for lack of oxygen.
Understanding these changes could help improve both organ transplants; also forensic investigations in the future. Dr. Marina Mora Ortiz, Post doctoral Research Associate in the Department of Twin Research at Kings College London; who carried out the research while at the University of Reading said. The paper gives us an interesting new concept for how we can look at changes in organ function; so after death and especially in organs such as the liver and heart where there is such a requirement for transplants.