Vasopressin is a hormone that promotes the reabsorption of water by the body. The level of vasopressin in the blood is considered normal if it is less than $2.5 \mu\mathrm{g}/\mathrm{mL}$. This hormone is secreted as soon as blood volume decreases. In particular, vasopressin is produced following a hemorrhage.
The following model will be used:
$$f(t) = 3t\mathrm{e}^{-\frac{1}{4}t} + 2 \text{ with } t \geqslant 0$$
where $f(t)$ represents the level of vasopressin (in $\mu\mathrm{g}/\mathrm{mL}$) in the blood as a function of time $t$ (in minutes) elapsed after the start of a hemorrhage.
- a. What is the level of vasopressin in the blood at time $t = 0$? b. Justify that twelve seconds after a hemorrhage, the level of vasopressin in the blood is not normal. c. Determine the limit of the function $f$ as $t \to +\infty$. Interpret this result.
- We admit that the function $f$ is differentiable on $[0; +\infty[$.
Verify that for every positive real number $t$,
$$f^{\prime}(t) = \frac{3}{4}(4 - t)\mathrm{e}^{-\frac{1}{4}t}$$
- a. Study the direction of variation of $f$ on the interval $[0; +\infty[$ and draw the variation table of the function $f$ (including the limit as $t \to +\infty$). b. At what time is the level of vasopressin maximal? What is this level then? Give an approximate value to $10^{-2}$ near.
- a. Prove that there exists a unique value $t_0$ belonging to $[0; 4]$ such that $f(t_0) = 2.5$. Give an approximate value to $10^{-3}$ near. We admit that there exists a unique value $t_1$ belonging to $[4; +\infty[$ satisfying $f(t_1) = 2.5$. An approximate value of $t_1$ to $10^{-3}$ near is given: $t_1 \approx 18.930$. b. Determine for how long, in a person who has suffered a hemorrhage, the level of vasopressin remains above $2.5 \mu\mathrm{g}/\mathrm{mL}$ in the blood.
- Let $F$ be the function defined on $[0; +\infty[$ by $F(t) = -12(t + 4)\mathrm{e}^{-\frac{1}{4}t} + 2t$. a. Prove that the function $F$ is an antiderivative of the function $f$ and deduce an approximate value of $\int_{t_0}^{t_1} f(t)\,\mathrm{d}t$ to the nearest unit. b. Deduce an approximate value to 0.1 near of the average level of vasopressin, during a hemorrhagic accident during the period when this level is above $2.5 \mu\mathrm{g}/\mathrm{mL}$.